Figure 40: Schematic Representation of a Gravitational Tank Irrigation System.

Source: V.N. Garc Dise Aplicaciel Riego Intermitente por Gravedad. Universidad Nacional Auta de Mco, Facultad de Ingenier Mco D.F., 1995 (Tesis para obtener el grado de Doctor en IngenierHidrica).

The design of these systems must consider irrigation water use, available hydraulic load, topographic characteristics in the area of application, physical dimensions of the irrigated land, slope and location of furrows, and soil characteristics. Design manuals, based on laboratory and field experiments, have been developed in Mexico.

Extent of Use

This technology has been used primarily in the arid and semi-arid regions of Mexico. The diabeto can be used in any gravity irrigation system, but has been particularly useful in the irrigation of 100 to 300 m² fields, using furrow irrigation, and in domestic gardening. This technology is best suited for small-scale (< 4 ha) irrigation in rural areas. At present, it is widely used only in Mexico.

Operation and Maintenance

The diabeto and the gravitational tanks with bottom discharges function automatically, based on flow control devices, and do not need outside energy sources. The water is discharged into a channel that distributes it into the furrows and to the irrigated crops. Maintenance is very simple, requiring only periodic cleaning of the tanks, siphons, and/or discharge pipes.

Level of Involvement

Up to now, educational institutions, small private agricultural enterprises, and the Mexican Government have promoted this technology. However, it would be desirable if local communities got more involved in implementing it,

Figure 41: Schematic Representation of an Automatic Fluid Water Control Device used in Gravitational Tanks.

Source: V.N. Garc Dise Aplicaciel Riego Intermitente por Gravedad, Universidad Nacional Auta de Mco, Facultad de Ingenier Mco, D.F. 1995 (Tesis para obtener e! grado de Doctor en IngenierHidrica).

Costs

A surge flow, automatic irrigation device such as the one shown in Figure 37 costs about $600. This includes an 11.25 m³ storage tank, feeding system, and siphon. A device of this size can irrigate up to 4 ha. A similar gravitational tank irrigation system, with the same tank capacity, 150 m of piping, and gates, has an estimated cost of $1 500. A smaller system for domestic gardening can cost around $80. The operation and maintenance costs of these systems are practically nil.

Effectiveness of the Technology

With the surge flow, automatic irrigation systems and the gravitational tank technologies, irrigation efficiencies of over 75% have been achieved in the state of Zacatecas, Mexico. This represents a significant improvement over the 25% rate reported using traditional irrigation technologies. A saving of about 25% in energy consumption costs has also been observed.

Suitability

The technology is recommended for arid and semi-arid areas where low precipitation and high evaporation rates prevail, and where small storage areas and depleted aquifers exist.

Advantages

· This technology can utilize water from small wells of limited capacity, reused wastewater, and small streams.

· Hydraulic energy is used as the driving force; these systems do not require external energy sources.

· The systems are low-pressure.

· Irrigation time and labor force requirements are small, as the systems are automatic.

· The technology is low in cost.

· It is easy to operate and maintain.

· It is applicable to small-scale agricultural systems.

· It is more efficient than traditional irrigation systems.

Disadvantages

· The technology is not recommended for furrow irrigation in fields with dimensions greater than 200 m long and 25 meters wide, as the volume of water required in such applications will require extremely large storage tanks.

· For greater efficiency, the irrigated lands should be leveled.

Cultural Acceptability

The technology has been tried and tested in Mexico, although it has the potential to be used in many other countries. Governments and international institutions can help disseminate information on its use.

Further Development of the Technology

To improve the applicability of this technology to areas using drip irrigation, a device that will automatically mix fertilizers into the water stream provided by the diabeto is under development. Also, development of modular systems is under way. Ultimately, the development of educational programs on the implementation and effective use of this technology will be necessary.

Information Sources

Contacts

Polioptro Martz Austria, Instituto Mexicano de Tecnologdel Agua, Coordinacie TecnologHidrica, Paseo Cuahunac 8532, 62550 Jiutepec, Morelos, Mco. Tel. (52-73)19-3663. Fax (52-73)20-8725. E-mail: polioptr@tlaloc.imta.mx.

Alvaro Aldama Rodrez, Instituto Mexicano de Tecnologdel Agua, Paseo Cuahunac 8532, 62550 Jiutepec, Morelos, Mco. Tel. (52-73)19-3663. Fax (52-73)20-8725.

NahrcVanueva, Instituto Mexicano de Tecnologdel Agua, Subcoordinacie Hidrica Rural y Urbana, Paseo Cuahunac 8532, 62550 Jiutepec, Morelos, Mexico. Tel. (52-73)19-4000, ext. 510.

Josatividad Barrios Domuez,, Universidad Auta de Zacatecas, Facultad de Ingenier Zacatecas, Mco.

Bibliography

Bishop, A.A., et al. 1981. "Furrow Advance Rates Under Surge Flow Systems." Journal Irrigation and Drainage, vol. 107. IR3.

Biswas, A.K. 1992. "Sustainable Water Development: a Global Perspective," Water International, 17(2).

Biswas, A.K. 1995. "Institutional Arrangements for International Cooperation in Water Resources," International Journal of Water Resources Development, 11(2).

FAO. 1990. An International Action Programme on Water and Sustainable Agricultural Development. Rome.

Garc V.N. 1995. Dise Aplicaciel Riego Intermitente por Gravedad. Mco, D.F., Universidad Nacional Auta de Mco, Facultad de Ingenier (Tesis para obtener el grado de Doctor en IngenierHidrica)

Jensen, M.E. 1990. "Arid Lands Impending Water Population Crises." In Proceedings of the ASCE International Symposium on Hydraulics/Hydrology of Arid Lands, (San Diego, Cal.). Reston, VA., ASCE.

Martz Austria, P. 1994. "Efficient Use of Irrigation Water." In Gardund Arreguin (eds.). Efficient Water Use, Chapter 4. Urbana, Ill., International Water Resources Association.

Martz Austria, P., and R. A. Aldama. 1990. "A Simple Fluidic Device for Surge Flow Irrigation." Paper presented to the XXIV Congress of the International Association for Hydraulic Research, Madrid. 9-13 September.

Martz Austria, P., and A. Aldama. 1990. Dispositivo Fluco para Riego Intermitente, Jiutepec, Morelos, Mco, Instituto Mexicano de Tecnologdel Agua. (Serie DivulgaciNo. 26)

Martz Austria, P., and A. Aldama. 1991. "Dispositivo de Control para la Aplicaciel Riego Intermitente." Revista IngenierHidrica en Mco, mayo-agosto.

Schiller, E.J. 1992. "Water Resources: An Emerging Crisis. Sustainable Water Resources Management in Arid Countries," Canadian Journal of Development Studies, Special Issue, pp. 7-12.

Stringham, G.E., and J. Keller. 1979. "Surge Flow Automatic Irrigation." Paper presented to the ASCE Irrigation and Drainage Specialty Conference, Albuquerque, N.M., U.S.A.

4.4 Dual water distribution

As the name implies, dual distribution systems involve the use of water supplies from two different sources in two separate distribution networks. The two systems work independently of each other within the same service area. Dual distribution systems are usually used to supply potable water through one distribution network and non-potable water through the other. The systems would be used to augment public water supplies by providing untreated, or poorly treated, water for purposes other than drinking. Such purposes could include fire-fighting, sanitary flushing, street cleaning, or irrigation of ornamental gardens or lawns. This system has been used in some Caribbean islands like Saint Lucia and the U.S. Virgin Islands.

Technical Description

The systems are designed as two separate pipe networks: a potable water distribution system, and a system capable of distributing sea water or other non-potable waters. The system includes distribution pipes, valves, hydrants, standpipes, and a pumping system, if required. Pipes in the systems are generally cast iron or ductile iron, although fiberglass has also been used.

In seawater-supplied systems, pumps are required to lift the seawater to higher elevation storage tanks. Likewise, pumps may be required to lift wastewaters from wastewater sumps or other collection points. The pumping systems consist of a pumping station containing the water intake, a pumping well, and an elevated storage tank for emergency use. The pumps require foot valves, or one-way valves, in order to retain their charge of water. The water is pumped through a manifold into the secondary or alternative distribution system.

The potable-water, or primary, system operates like any other potable-water supply and distribution system, requiring a water source, treatment plant, storage facility, and distribution system. Pumps are generally required to lift potable water from the treatment plant to storage tanks, from which it is distributed by gravity to the point of use.

Extent of Use

This technology is rarely used. Seawater-based systems have been used in Castries, Saint Lucia, for fire-fighting purposes and in Charlotte Amalie, U.S. Virgin Islands. U.S. Navy bases have installed and operated similar systems in the past. Wastewater-based systems are discussed in Chapter 3, "Wastewater Treatment Technologies and Reuse."

Operation and Maintenance

Depending on the use (i.e., intermittent use in the case of fire-fighting supplies or regular in the case of irrigation supplies) and water source used (e.g., seawater or wastewater), in the dual distribution system, regular testing of the system is recommended. The seawater-based system used in the U.S. Virgin Islands was tested daily in the past, but is now tested once a week. The pumps are turned on and a by-pass is used to allow the return of seawater to the sea to avoid pressurizing the distribution system. The pumps and engines are routinely serviced according to manufacturers' specifications.

Problems experienced in the operation and maintenance of this system include accidental damage to foot valves and standpipes. In the case of seawater systems, ships have been known to damage foot valves located in the harbor, and, in the case of the distribution systems, vehicles frequently damage hydrants and standpipes, which then have to be replaced. In addition, foot valves require frequent servicing to remove fungal and other growths which can prevent their proper opening and closing and can make it impossible for the pumps to maintain their charge. On the landward side, regular inspection and maintenance of the standpipes and hydrants is required to remove debris from the openings of the hydrants and standpipes, which become clogged as a result of vandalism (persons pushing debris into the hydrant openings). It is also necessary to ensure that the pump engines are supplied with adequate reserves of oil and fuel, and that the pumps and motors are properly lubricated for optimal operation.

Level of Involvement

The systems arc entirely a government-run operation in most cases. In Saint Lucia, the fire department had direct involvement in the implementation of this technology, which supplies non-potable water for fire-fighting purposes. Variations on this system, involving the reuse of process water, have been implemented by specific industries as a means of reducing their use of raw water.

Costs

The cost of constructing a new distribution system for seawater (capital costs) would be similar to that for laying regular distribution pipelines (approximately $4/ft of pipe). In effect, the installation of a dual distribution system approximately doubles the cost of construction of the distribution system, although some savings may be achieved if the two systems are installed at the same time (instead of in series, with the non-potable system retrofitted into an existing distribution system).

Pumping costs (operation and maintenance costs) are also similar to those incurred by a typical water utility. For systems that are used intermittently, these costs would only be incurred on the few occasions when fire necessitates pumping and/or when pumps are being tested.

Effectiveness of the Technology

This technology is highly effective. Seawater is as effective as potable water when used for fire-fighting purposes, but does not result in the drawdown of potable supplies. The system installed in Castries provides sufficient urban coverage and adequate supplies of water to fight most fires in the city. In contrast, public support for the dual distribution system in the U.S. Virgin Islands has diminished, making the system more prone to vandalism and less effective overall.

Suitability

The technology is suitable only in areas where a supply of raw water is available. This type of system is generally used near the coast where seawater is abundant, or in places where wastewater is readily available as a source of supply. It can also be utilized in areas that have rivers, streams, or other water sources but lack treatment facilities; in other words, in areas supplied with public water but having access to additional water sources that would otherwise go unutilized or underutilized.

Advantages

· This technology allows the use of cheaper sources of water for non-consumptive purposes, which may currently be served from more expensive, and limited, potable water supplies.

· If used to augment the regular distribution system, it makes more potable water available to the general public.

Disadvantages

· A dual distribution system requires that two distribution systems have to be installed, at essentially double the cost of a single system.

· Having non-potable water in a distribution system creates a potential to cross-contaminate the potable water system (while this is of limited concern in seawater systems, accidental consumption of non-potable water from wastewater-based systems could have serious consequences).

· Use of untreated seawater or wastewater to irrigate leafy vegetables could also threaten human health.

· Seawater can be highly corrosive to metal pipes, fittings, and appurtenances; it increases maintenance costs associated with distribution lines and affects toilet and other metal fixtures that come into contact with the water.

· If return flows enter the wastewater stream, the introduction of large volumes of seawater to treatment plants make sewage treatment more difficult since the salts can impair the effectiveness of activated sludge reactors or rotating biofilters, for example.

Cultural Acceptability

This technology is accepted as a alternative for the supply of non-potable water for use in firefighting, street cleaning, etc. It is generally best suited to areas having a plentiful alternative source of water such as seawater or wastewater. In the latter case, concerns about possible human health effects may arise.

Further Development of the Technology

Development and use of non-corrosive materials, such as fiberglass, may make this technology more attractive, especially in cases where seawater is the principal source of non-potable water used in the dual distribution system. The use of alternative materials such as PVC in components such as foot valves might reduce potential for fungal growth and other growths that clog or damage the valves. There is also a great need for public awareness, among users, plumbers, and others, to minimize cross-connections and other potential sources of cross-contamination of the potable water supply.

Information Sources

Contacts

Vincent Sweeney, c/o Caribbean Environmental Health Institute (CEHI), Post Office Box 1111, Castries, Saint Lucia, Tel. (809)452-2501. Fax (809)453-2721. E-mail: cehi@isis.org.lc.

Primus Duplessis, Chief Fire Officer, Fire Service, Ministry of Home Affairs, Castries, Saint Lucia. Tel/Fax (809)452-3064.

Henry H. Smith, Director, Water Resources Research Institute, University of the Virgin Islands, #2 John Brewers Bay, St. Thomas, U.S. Virgin Islands 00802-9990. Tel. (809)693-1063. Fax (809)693-1074. E-mail: hsmith@uvi.edu.

4.5 Other water conservation practices

The importance of water conservation and water loss reduction should always be an integral part of the management of freshwater resources and needs to be given prominence in freshwater resources planning. As is suggested by the three interlinking arrows in the recyclable materials symbol, reduction of waste is the first of the several means of resource conservation (the other means being reuse and recycling, both of which are covered elsewhere in this volume). An excellent reference book is Efficient Water Use, edited by Hector Gardund Felipe ArreguCort.

For water management purposes, the community can be divided into two basic groups: system users (such as households, industry, and agriculture) and system operators (such as municipal, state, and local governments and privately owned suppliers). These users have a choice of a number of different practices, which promote or enhance the efficiency of their use. These practices fall into two basic categories: engineering practices, based on modifications to hardware (e.g., plumbing and fixtures) and/or water supply operational procedures, and behavioral practices, based on changing water use habits.

Engineering practices are generally technical or regulatory measures, while behavioral practices typically involve market-oriented measures. Collectively, these measures, which affect water use and reduce waste and loss from the source, are known as "demand management" measures. Such measures include leak detection; waste reduction (encouraging consumers to cut out wasteful uses); investment in appliances, processes, and technologies that reduce water input without reducing consumer satisfaction and/or output; treatment of industrial effluents and wastewaters to a standard suitable for recycling and reuse; and reallocation of freshwater resources to the area of greatest social good. The policies that encourage demand management include pricing water at an economic rate, charging for pollution or community-based pollution control practices, regulating and restricting specific water uses, exhorting and informing the consumer of the ways and means of use reduction and recycling, and encouraging water trading among and between users.

Figure 42: Typical Breakdown of Interior Water Use.

Source: USEPA, Cleaner Water Through Conservation, Washington, D.C., 1995 (Report No. EPA- 841/B-95-002).

Technical Description

Water conservation practices can be followed by residential users, industrial and commercial users, and agricultural users. They can also be followed by local utilities and/or regional water supply plants. Table 21 shows some of the more common practices recommended for use by the different user groups. A brief description of the most common conservation practices follows.

Table 21 - Recommended Water Conservation Practices

Source: USEPA, Cleaner Water Through Conservation, Washington D.C., 1995 (Report No. EPA-841/B-95-002).

· Residential Users Conservation Measures

Low-flow plumbing fixtures and retrofit programs are permanent, one-time conservation measures that can be implemented with little or no additional cost over the lifetime of the fixtures. In some cases, these fixtures can even save the residents money over the long term. The most commonly recommended low-flow plumbing fixtures are pressure reduction devices, faucet aerators, toilet displacement devices, low-flush toilets, low-flow showerheads, and plumbing modifications for gray water reuse. A typical breakdown of residential water use is shown in Figure 42.

Pressure Reduction. Homeowners can reduce the water pressure in a home by installing pressure reducing valves. A reduction in water pressure can save water in other ways: it can reduce the likelihood of leaking water pipes, leaking water heaters, and dripping faucets.

Faucet Aerators. Faucet aerators, which break the flowing water into fine droplets and entrain air while maintaining wetting effectiveness, are inexpensive devices that can be installed in sinks to reduce the volume of water used. Aerators are easily installed and can reduce the volume of water use at a faucet by as much as 60% while still maintaining a strong flow. More efficient kitchen and bathroom faucets that use only 7.5 l/min, in contrast to standard faucets, which use 12 to 20 l/min, are also available.

Toilet Displacement Devices. Non-toxic bricks or plastic containers (e.g., milk jugs filled with water or pebbles) can be placed in a toilet tank to reduce the amount of water used per flush. By placing between one and three such containers in the tank, more than 4 l of water can be saved per flush. A toilet dam, which holds back a reservoir of water when the toilet is flushed, can also be used instead of the displacement device to save water.

Low-Flush Toilets. Conventional toilets use 15 to 201 of water per flush, but low-flush toilets use only 61 of water or less. Since low-flush toilets use less water, they also reduce the volume of wastewater produced. A schematic of a low-flush toilet is shown in Figure 43. Even in existing residences, replacement of conventional toilets with low-flush toilets is a practical and economical water-saving alternative.

Low-Flow Showerheads. Showers account for about 20% of the total indoor water use in an household. By replacing the standard 18 l/min showerheads with 10 l/min showerheads, which cost less than $5 each, a family of four can save approximately 80,000 l/year. Properly designed low-flow showerheads, currently available, are able to provide the quality of water delivery found in higher volume models.

Gray Water Use. Domestic wastewater composed of washwater from kitchen sinks and tubs, clothes washers, and laundry tubs is called gray water. Gray water can be used by homeowners for home gardening, lawn maintenance, landscaping, and other uses that do not require potable water. The level of contamination of gray waters is minimal; however, the plumbing modifications needed to make use of this water should not allow its contamination by wastes from the toilets, which have the potential to spread disease, cause undesirable odors, and result in aesthetic degradation of homestead yards and gardens.

Figure 43: Gravity Design of a Low-Flush Toilet.

Source: USEPA, Cleaner Water Through Conservation, Washington B.C., 1995 (Report No. EPA-841/B-95-002).

1. The 6 liter flush design of this gravity toilet has a different flush mechanism.

2. Steep bowl sides and a narrow trapway to allow the siphoned water to gain velocity for more effective removal of waste.

3. This is where the water pushes waste into the trapway.

4. Stored water flows into the bowl.

· Landscaping Water Conservation Practices

Drought-Tolerant Plants. Water conservation in landscaping can be accomplished through the use of plants that need little water, thereby saving not only water but labor and fertilizer as well. Careful landscape design can significantly reduce water use; it can also take advantage of native plants which have evolved water-saving or water-tolerant characteristics ideally suited for the local climatic conditions. Use of native plants can also help to minimize the spread of exotic plant species that disrupt local ecosystems. In addition to the selection of the plant species to be used in landscaping, practices such as the use of low precipitation rate sprinklers that have better distribution uniformity, bubbler/soaker systems, and/or drip or point irrigation systems can also conserve water used for landscaping purposes.

Xeriscaping. Xeriscaping is an innovative approach to landscaping that promotes water conservation and pollution prevention. Traditional landscapes might incorporate one or two principles of water conservation, but xeriscaping uses planning and design, soil analysis, selection of suitable plants, practical turf areas, efficient irrigation, use of mulches, and appropriate maintenance to create an appropriate landscape for a given climatic condition. Xeriscaping is most successfully practiced in arid and semi-arid areas, where it has proved useful for minimizing irrigation and external maintenance needs while presenting an attractive appearance.

· Agricultural Water Conservation Practices

Water saving irrigation practices fall into three categories: field practices, management strategies, and system modifications. Examples of these practices include, respectively, the chisel plow aeration of extremely compacted soils, furrow diking to prevent uncontrolled runoff, and leveling of the land surface to distribute water more evenly. A number of these practices have been previously detailed in chapters 2 and 3.

Irrigation Scheduling. Improved irrigation scheduling can reduce the amount of water required to irrigate a crop effectively by reducing evaporative losses, supplying water when most needed by the irrigated plants, and applying the water in a manner best suited to the plants being irrigated. A careful choice of the rate and timing of irrigation can help farmers to maintain yields with less water. In making scheduling decisions, irrigators should consider:

· The uncertainty of rainfall and the timing of crop water demands.
· The limited water storage capacity of many irrigated soils.
· The finite pumping capacity of most irrigation systems.
· The price of water and changes in water prices as additional operators increase water demand.

Irrigation Management. Management strategies involve monitoring soil and water conditions and collecting information on water use and efficiency. The methods include measuring rainfall, determining soil moisture levels, monitoring pumping plant efficiency, and scheduling irrigation. Typical system modifications include the addition of drop tubes to a center pivot irrigation system, retrofitting wells with smaller pumps, installing a surge or demand irrigation system, and/or constructing a tailwater or return flow recovery system.

· Industrial and Commercial Users Water Conservation Practices

Water recycling is the reuse of water for the same application for which it was originally used. Recycled water might require treatment before it can be reused. Cooling water recirculation and washwater recycling are the most widely used water recycling practices. The following guidelines should be used when considering water reuse and recycling in industrial and commercial applications:

· Identification of water reuse opportunities: Are there areas within the factory or in the production process that currently use water only once that would be amenable to reuse?

· Determination of the minimum water quantity needed for the given use: Are there areas within the factory or in the production process where more water is being supplied than is needed to accomplish the purpose?

· Identification of wastewater sources that satisfy the water quality requirements: Does the process require potable water or water of a lesser standard? Can the same result be achieved with lower-quality water?

· Determination of how the water can be transported to the new use: What modifications, if any, in the process or factory may be needed to permit recovery and recirculation/recycling of the water currently sent to waste? What additional treatment may be necessary to reuse this water? What is the relative cost of the required modifications versus the cost of the raw water over the life of the modifications?

Cooling Water Recirculation. Recycling water within a recirculating cooling system can greatly reduce water consumption by using the same water to perform several cooling operations. The water savings are generally sufficiently substantial to result in an overall cost saving to industry. Such savings can be even greater if the waste heat is used as a heat source elsewhere in the manufacturing process. Three cooling water conservation approaches are typically used to reduce water consumption: evaporative cooling, ozonation, and heat exchange.

Washwater Recycling. Another common use of water by industry is in the use of fresh or deionized water for removing contaminants from products and equipment. Deionized water can generally be recycled after its first use, although the reclamation treatment cost of recycling this water may be as great as or greater than the cost of purchasing raw water from a producer and treating it. The same processes required to produce deionized water from municipal water can be used to produce deionized water from used washwater. It is also possible to blend used washwater with raw water, which also would result in an overall water saving. The reuse of once-used deionized water for a different application within the same factory should also be considered as a water conservation option. For example, used washwater may be perfectly acceptable for washing vehicles or the factory premises.

· Water Conservation Practices for Water Utilities

Common practices used by water supply utilities include metering, leak detection, repairing water lines, well capping, retrofitting programs, pricing, wastewater reuse, and developing public education programs and drought management plans.

Metering. The measurement of water use with a meter provides essential data for charging fees based on actual customer use. Submetering may also be used in multiple-unit operations such as apartment buildings, condominia, and mobile homes to indicate water use by individual units within a complex. In such cases, the entire complex of units might be metered by the main supplier, while the individual units might be monitored by either the owner or the water utility.

Leak Detection. It has been estimated that in many distribution systems up to half of the water supplied by the water treatment plant is lost to leakage; even more may be lost due to unauthorized abstraction. One way to detect leaks and identify unauthorized connections is to use listening equipment to survey the distribution system, identify leak sounds, and pinpoint the locations of hidden underground leaks. Metering can also be used to help detect leaks in a system. It is not unusual for unaccounted water losses to drop by up to 36% after the introduction of metering and leak detection programs.

Water Distribution Network Rehabilitation. A water utility can improve the management and rehabilitation of its water distribution network by a well-planned preventive maintenance program based on a sound knowledge of the distribution network. This knowledge is often embodied in a distribution system database that includes the following data:

· An inventory of the characteristics of the system components, including information on their location, size, and age and the construction material(s) used in the network.

· A record of regular inspections of the network, including an evaluation of the condition of mains and degree of corrosion (if any).

· An inventory of soil conditions and types, including the chemical characteristics of the soils.

· A record of the quality of the product water in the system.

· A record of any high or low pressure problems in the network.

· Operating records, such as of pump and valve operations, failures, or leaks, and of maintenance and rehabilitation costs.

· A file of customer complaints.

· Metering data.

Through the monitoring of such records, advance warning of possible problems can be achieved. For example, excessive water use, or numerous complaints or demands for spare parts, could be early warning signs of an impending breakdown in the system. This system should also include a regular program of preventive maintenance to minimize the possibility of system failures.

Well Capping. Well capping is the sealing of abandoned wells. In the case of artesian wells, rusted casings can spill water in a constant flow into drainage ditches, resulting in evaporative loss or runoff losses, in non-artesian wells, uncapped abandoned wells form points of entry for contaminants into the groundwater system.

Pricing. Placing an economic value on freshwater is the principal means of achieving water conservation. Pricing provides a financial incentive to conserve water. Rate structures may be variable and/or graduated, with prices fixed on the basis of class of service (residential versus industrial or agricultural, for example) and quantity used (for example, the unit price for quantities below 400 l/day might be significantly lower than for quantities which exceed that amount for a single-family residence). Pricing has the advantage of minimizing the costs of overt regulation, restrictions, and policing, while providing a high degree of freedom of choice for individual water customers.

Retrofit Programs. Retrofitting involves the replacement of existing plumbing fixtures with equipment that uses less water. The most successful water-saving fixtures are those which operate in the same manner as the fixtures being replaced; for example, toilet tank inserts, faucet aerators, and low flow showerheads do not significantly change the operation of the systems into or onto which they are placed, but they do result in substantial water savings.

Water Audit Programs. Various types of audits can be undertaken. For example, residential water audits may involve sending trained water auditors into participating households, free of charge, to encourage water conservation efforts, or providing them with record sheets to note down their water use for external analysis. Water audits may also be undertaken in commercial and industrial facilities, and may be combined with an assessment of the potential for implementing water reuse and recycling programs. A pre-implementation and post-implementation water audit in factories adopting a reuse and recycling program would be a valuable means of demonstrating and quantifying the water savings achieved.

Public Information and Education. Public information and education programs can be undertaken to inform the public about the basics of water use and conservation. Programs should be developed for specific applications and may be targeted at specific user groups or age groups; for example, at housekeepers, to encourage domestic water conservation, or at schoolchildren, to provide information on the wider implications of water conservation for future consumption, the environment and other uses. Basic information should include the following:

· How water is delivered and how wastewater is disposed of.
· The costs of water and water supply services.
· Why water conservation is important.

The programs should provide guidance on how the user groups and individuals can participate in conservation efforts. It should be noted that there is a large body of public information and education materials available, particularly in the United States, which may be obtained from a variety of public agencies and NGOs at little or no cost and form the basis of a local public awareness initiative.

· Drought Management

Given the vagaries of the modem climate, in this period of climate change, it seems that droughts may be more severe or extensive than is the past. Many water conservation projects constructed to alleviate drought-induced water shortages are themselves victims of drought. Whether this may simply reflect changes in land use within a watershed that allow less water to infiltrate into the groundwater system, or results from population growth, which places greater demands on finite water resources, is not clear and rarely proved. In any case, many communities are currently experiencing a need to have drought management plans in place to ensure the greatest possible availability of freshwater during periods of below average rainfall.

Drought Management Planning. When rainfall is less than usual, there is less water to maintain normal soil moisture levels, stream flows, and reservoir levels and to recharge groundwater. Because of these varied sources and the multiple demands placed upon freshwater resources, a drought management plan should address a range of issues, from political and technical matters to public involvement. Some of the components of a typical drought management plan include the following:

· Identification of the available water resources.

· Tabulation of the multiple sectoral demands for freshwater.

· Description of possible shortfalls between supply and demand.

· Definition of the management measures required for various eventualities, and an agreed allocation schedule in the event that water rationing becomes necessary.

· Provision for user and public involvement in the drought management program.

· Promulgation of legislation, agreements, rules, and procedures to ensure a timely and equitable response to the onset of drought conditions.

· Issuance of a drought management event plan and public information materials to make it known.

Demand Management. Demand management is closely linked with water conservation practices. Table 22 shows, in summary form, short-term measures that can be used to reduce demand during periods of drought and the expected levels of reduction. These measures may also be considered in concert with other conservation measures noted above.

Table 22 - Short-Term Measures to Reduce Water Demand and Their Effectiveness

Source: Ramesh Bhatia, et al., Water Conservation and Reallocation: Best Practice Cases In Improving Economic Efficiency and Environmental Quality, Washington, D.C., World Bank, 1995 (A World Bank-ODI Joint Study).

Extent of Use

Water conservation measures have been practiced primarily in the United States, although some Latin American countries have implemented specific measures. For example, in Brazil, the pharmaceutical, food processing, and dairy industries were required to pay effluent charges that contributed to reductions in water use and wastewater production of between 42% and 62%. In Mexico, increased water prices contributed to an increase in wastewater reuse and the recycling of cooling water.

Chile is the only country in the region with a comprehensive water law that has encouraged the development of water markets. The 1981 National Water Law established secure, tradable, and transferable water use rights for both surface and groundwaters. As a result, during periods of low rainfall, farmers shift from the production of water-intensive crops, such as corn and oilseeds, to higher-valued and less water-intensive crops, such as fruits and vegetables.

Water recycling is used at a Container Corporation of America Mill in Santa Clara, California (U.S.A.), that manufactures paperboard from the recycled fibers of newspapers, corrugated cardboard clippings, and ledger paper. Historically, water has been used in this process for a variety of purposes. In recent years, however, the mill has begun recycling water used in its rinsing processes after clarification. The mill has also installed a closed loop cooling tower, which has resulted in an additional reduction in water use. These water conservation and use efficiency practices have resulted in an estimated saving of approximately 2.8 million l/day, compared to its 1980 water use rates. These water reductions amount to approximately 900 million l/year and saved the company approximately $348 200 per year.

Operation and Maintenance

Given the variety of measures that might be undertaken to address conservation needs within a specific geographic area, of which a number are mechanical but many may be technological or informational, it is difficult to identify specific operational requirements. However, some of the more obvious requirements include the following: low-flow water conservation devices require periodic maintenance and repair; leak detection equipment and meters require periodic testing and repair; drought and water conservation management strategies, such as pricing and user charges, require monitoring and enforcement; and well-capping programs require monitoring and trained personnel in order to be effective. Maintenance requirements range from regular inspections of mechanical devices to the review of legislation and conservation plans to ensure their continued relevance.

Level of Involvement

The installation and maintenance of low-flow household and irrigation devices may require governmental incentives in order to be accepted. In some cases, employees of the water utility may install and maintain these systems at little or no charge in order to effect the desired water savings. Alternatively, government regulations may be necessary to provide incentives for the implementation of industrial and agricultural water conservation measures. Government action is required in the promulgation of plumbing codes for new construction that will contribute to the adoption of residential water conservation measures. Government or utility involvement is also needed for leakage detection and the repair of distribution systems. Metering, in addition to requiring technical personnel and equipment to be effective, generally requires governmental action to implement and government authority to establish or regulate water tariffs. However, community participation and voluntary conservation are a key element if this technology is to be effective.

Costs

The cost of water conservation measures varies with the cost of any equipment required and with size and location. The cost of replacing a conventional toilet with a low-flush toilet is about $250 per unit. Low-flow showerheads, in contrast, cost about $5 each. Meter installation costs range from about $200 for interior meters to $500 for external meters. Leak control has been estimated at $40/million liters.

Costs associated with water conservation are often offset by cost savings incurred after implementation. For example, the use of treated wastewater for cooling at an industrial plant in California, U.S.A., resulted in a saving of $150 000 in 1989, while modifications to the sinks in a computer manufacturing plant in Denver, Colorado, resulted in a saving of $81 000, also in 1989. Close monitoring of water use in a packing facility in Santa Clara, California, produced an annual saving of $40 000. Elsewhere, the introduction of water markets in Chile in 1993 increased agricultural profits by $1.5 billion.

Effectiveness of the Technology

Water conservation measures are highly effective. However, this technology may not be too popular with consumers, who may be asked to pay a higher price for the water they consume, and can be, politically, very unpalatable. Nevertheless, studies carried out in Seattle, Washington, U.S.A., reported the following results from water conservation measures:

· According to detailed data on the performance of low-flow water devices in 308 single-family residences, indoor per capita water use dropped 6.4% after low-flow showerheads were installed.

· Easily installed aerators reduced water use at a faucet by as much as 60% while still maintaining a strong flow.

· A reduction in water pressure from 100 pounds per square inch (psi) to 50 psi at an outlet resulted in a water flow reduction of about one-third of the pre-existing use.

· Gray water reuse saved a volume of water equivalent to that needed to supply more than 7 000 residences and businesses.

· Outdoor water use was reduced by restricting watering times to the early morning or late evening; watering on cooler days, when possible, also reduced outdoor water use. All these measures contributed to reduced evaporative losses.

· As many as 600 l of water were saved when washing a car by turning the hose off between rinses; additional benefits and water savings were achieved by washing the car on the lawn, which both watered the lawn and reduced runoff.

· Sweeping sidewalks and driveways, instead of hosing them down, saved about 200 l of water every 5 minutes.

In other studies, such as an industrial water conservation project in California, the conversion of an industrial process from a single-pass freshwater cooling system to a closed-loop cooling system, with circulating chilled water, has saved an estimated 20 000 to 28 000 l/day, while cities in the hemisphere that have large, old, deteriorating systems, leak detection programs have been especially efficient in minimizing water losses.

Suitability

Water conservation measures are suitable and recommended for all public water supply systems, industries with high water use, agricultural enterprises, and individual residential users in Latin American countries and the Caribbean islands.

Advantages

Residential water users:

· Low-flow devices result in water use savings of 20% to 40%.
· Pressure reductions save up to 33% of the water normally consumed.
· Conservation-based landscape irrigation practices also produce significant water use savings.

Industrial/commercial users:

· Water recycling greatly reduces water use.

· Deionized water can be recycled after its first use at little or no additional cost, using the same equipment used to produce the deionized water from the municipal supply.

· Proper scheduling of landscape irrigation optimizes water use by minimizing evaporative losses.

Agricultural users:

· Water savings can be achieved through a combination of field practices, monitoring, and system modifications.

· Wastewater reuse can produce significant water savings.

Water supply plants:

· Widespread leakages and illegal connections may account for 30% to 50% of the water loss in a distribution system.

· Metering allows for greater accountability and assists in the development of a pricing structure that is fair and appropriate to the individual water supply system and that provides incentives for conservation.

· Equipment repairs to water mains and valves, and capping unused wells, can reduce unnecessary water loss, and prevent contamination of both piped water and groundwater.

· Retrofit programs can produce long-term savings of water and money.

Disadvantages

Residential users:

· The initial cost of low-flow devices can be high.
· Changes or modifications in water use habits are not readily accepted.

Agricultural users:

· Low-volume irrigation systems may be costly in some cases.
· The use of wastewater for irrigation may pose potential health risks.

Industrial/commercial users:

· Modifications to manufacturing processes may be required in some cases, incurring an initial capital charge to the user.

· Changes in the piping system within a plant can be costly.

Water supply plants:

· Implementation of leak detection, control and metering is costly.
· Meters and leak detection devices require regular maintenance.

Cultural Acceptability

Most conservation measures have been applied in response to government regulations or conservation programs. As was noted above, public acceptance is limited despite the economic benefits.

Further Development of the Technology

Improved equipment for use in leak detection and metering is required. Such devices need to be more robust and less costly. Meters should be able to withstand tampering. It would also be desirable for low-flow plumbing devices to be more cost effective so as to be more attractive to consumers. Implementation of educational programming on the necessity and the economic and environmental benefits of water conservation is also likely to lower consumer resistance to water conservation technologies.

Information Sources

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Table 23 - Summary of Alternative Technologies Presented in the Source Book

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