5. Results of the survey

The results of the survey are presented below in Table 2 in summary form and in greater detail in Parts B and C. Technologies have been considered in four focal areas; water conservation, wastewater treatment and reuse, freshwater augmentation, and upgrading the water quality of natural waters.

Water conservation technologies include: water recycling in industries (i.e., cleaning wastewater for reuse in the same or other processes), dual distribution systems with drinking water in one system and water of marginal quality for non-potable uses in another, and mono-molecular organic surface films on the surfaces of water storage reservoirs to reduce evaporative losses.

TABLE 2. Summary Evaluation of Alternative Technologies for Freshwater Augmentation in Asia.

Wastewater treatment and reuse technologies include: reuse of irrigation water by tapping return flows from the drainage system for further irrigation use downstream, the use of sewage effluent in aqua-culture (primarily the use of night soil and fecal-contaminated surface waters for fertilizing fish ponds, and irrigation), primary wastewater treatment (in which organic and inorganic materials are removed from waste water through sedimentation and filtering), secondary wastewater treatment (in which also the non-settleable solids are removed, primarily through biochemical processes, to promote the degradation of organic pollutants), advanced wastewater treatment such as carbon adsorption, microstraining, and desalination, and water treatment by lagoons and wetlands (as a form of secondary wastewater treatment utilizing the naturally occurring processes in these areas).

Freshwater augmentation technologies include: rainwater harvesting from roofs into jars and pots or small dams, fog and dew harvesting to condense air-borne moisture into liquid water for drinking water supplies or irrigation, small-scale water storage facilities including small ponds, tanks, surface reservoirs, and underground reservoirs formed by subsurface obstructions or dams, artificial groundwater recharge using infiltration from the surface or injection via deep wells, and cloud seeding.

Technologies for the upgrading of the quality of natural waters through desalinization include distillation, reverse osmosis and electrolyte systems.

5.1 Bangladesh

From time immemorial, rainwater has been playing a significant role in the socio-economic life of Bangladesh. In fact, the entire agro-economic fabric of the country is built on the particular rainfall pattern (commonly known as the monsoon) occurring ion the country. Nevertheless, very few studies have been carried out on rainwater harvesting. Those that are available are studies by Hossain and Ziauddin (1992), Sarker (1994), and Uttaran (1995). The major constraint on the development of rainwater harvesting technologies is a low education level of the people and the poor economic condition of their households. The past studies have provided few innovations for users in the methods of collection and storage of rainwater. A joint Department of Public Health Engineering (DPHE) and UNICEF programme, that has been working in the southern area of Bangladesh since 1984 to provide better quality drinking water, has been reported that, despite filtering, the water remained salty during the dry season and that people did not want to use it. Of the 90 DPHE-UNICEF sand-filtration facilities serving communities of 50 to 60 users, 45% were found to be idle.

In contrast, rainwater harvesting by the erection of bunds around farms is the most common and one of the earliest methods of rainwater harvesting in Bangladesh. In this method, earthen bunds with height of 30 to 45 cm and width of equal dimensions are constructed around the field. Farmers have learned from experience to match their cropping cycle with rainfall pattern. Rainwater meets around 78% to 97% of land preparation water requirement for aman crops. In saline areas, rainwater is used in the aman paddies to dilute saline river water until the river water becomes sweet. Over the entire aman crop cycle, rainwater meets around 50% of water requirements with the residual being obtained from river water sources.

Variations on this technology exist. In the upland areas of Bangladesh (NC zone- Jhenaighati, Nokla thanas) rainwater is stored in low lying plots usually in between two hills to be used in times of necessary. Plots are irrigated using traditional equipment such as dhoons and hicha. In the CW zone (Jhenaidah thana), rainwater is collected from surrounding lands at higher elevations and carded to storage ponds through a culvert. In saline areas (the Patuakhali, Khulna, Satkhira and Bagerhat districts), lands are located within polders or embankments erected to obstruct intrusion of saline water. In these areas, around three-quarters of the agricultural lands are being used for saline water-based shrimp culture delimiting options for freshwater based agriculture.

The polders also have the potential to revolutionize the drinking water supply systems in the saline areas (the greater Khulna, Satkhira, Patuakhali, Barisal and Noakhali districts) through the construction of "sweet water ponds" which are replenished by rainwater in the monsoon. In southern portion of Hatya and other remote islands in the Bay of Bengal, where there are very few tubewells, rainwater from these ponds is found to meet nearly 80% of the drinking water requirement in the monsoon season. In the saline area of the SW zone, rainwater meets 44% and 7% of drinking water requirement in monsoon and dry season, respectively. Ponds and tubewell water meet remaining 31% and 25% of monsoon season water drinking water requirement. Rainwater meets 49% of cooking water requirement in the monsoon season and is not used at all for bathing. On the other hand, in the NC zone, rainwater is not used for drinking purposes but, instead, is used for cooking (6%) and bathing/washing (11%). The bulk of the drinking, cooking and bathing/washing requirement is met from tubewells. In the NW zone, only 2% of the inhabitants reported using rainwater, for bathing only, as their entire requirement for drinking and cooking water is met from tubewells and, to some extent, from ponds/rivers and other surface waterbodies.

One of the oldest method of rainwater harvesting in Bangladesh is the use of roof-tops for collecting rainwater which is conveyed through a gutter to a pot, or motka, for immediate use or to a storage place for use later on. The water stored retains its colour and taste for around two months after monsoon, after which, the water gradually becomes contaminated with toads, mosquitos, cockroaches, etc. Previously, fish such as Koi, Singh or Magur (Anabas testudinews, Heteropreutes sp., and Clarias batrachus) were grown in the pots to eat the larvae of mosquitos and other insects. However, as these fishes discharge their own excreta in the water, which also degrades the quality of water, use of fish to maintain water quality is fast decreasing. Occasionally, alum or other locally made flocculant aid, like burnt shell, is used to purify the water. Water purifying tablets are very infrequently used.

Of the many industrial uses of harvested rainwater, one of the commonest is fish culture. In north Bengal and in Mymensingh, ponds are completely dried prior to the monsoon. The soil is enriched with lime and cow dung, and the water is treated with potash, to prepare the ponds for fish cultivation. In other areas, water is kept in the ponds at levels of 1 to 1.5 m prior to the monsoon. In saline areas like Hatiya, the same pond may be used for drinking water supply purposes. No soil treatments are applied to these ponds. In Sherpur District (Jhenaigati thana), rainwater is stored in embankments and used for fish culture. In the NC zone, excess water flowing out of the embankments passes through a net so that fish cannot escape from the pond.

5.2 India

The National Water Policy of India states that water is a prime natural resource, a basic human need and a precious national asset. It recommends that water resources planning be done for hydrological units, such as drainage basins or sub-basins. As far as possible, the projects should be planned and developed as multipurpose projects. Provision for drinking water should be given priority over other uses of water. The integrated and coordinated development of surface and ground waters and their conjunctive use should form an essential part of all water resources development projects, with recycling and re-use of water being an integral part of water resources development. Emphasis is placed on the preservation of the quality of the environment and ecological balance in planning, development and operation of water resources projects. The National Water Policy stresses the use of freshwater augmentation technologies as one means of alleviating India's chronic water shortages.

Water conservation may be achieved by modification of technologies and industrial processes in order to reduce the rate of water consumption. Better maintenance, interception and recovery of process water, and recycling can significantly contribute to water conservation efforts. Use of water of lesser quality, such as reclaimed wastewater, for cooling and as fire water can be an attractive option for large and complex industries to reduce their water costs, increase production and decrease the consumption of energy. This conserves better quality waters for potable uses. These technologies can be further complimented dew water harvesting or by constructing "dew ponds". The climatic conditions of some parts of Assam in Brahmaputra Valley and in hill areas hold promise for use of dew ponds. Public information programmes also contribute to water conservation in urban areas.

Agricultural water sources can be supplemented by small structures (pick ups) built across seasonal or perennial streams to check the flow of water at appropriate locations by constructing bunds using locally available materials like stones, boulders or even mud bunds turfed with a grass locally available (Maane hullu). Use of these structures results in water storage, groundwater recharge, prevention of soil erosion, and availability of water for other activities in areas where water would typically not be available for much of the year. In contrast, in the Krishna Delta, large demands for water from the Nagarjuna Sagar Reservoir have reduced the volume of freshwater reaching the Delta, and it has become necessary to utilize the groundwater supplies. In order to achieve an acceptable quality, however, groundwater must be used conjunctively with the limited surface water resources in a mix of 28:72, groundwater: surface water. Blending these waters should result in the conservation of storage in the reservoir of about 751 Mm³ for the first stage and 1 016 Mm³ for final stage, for a year with average inflows. In a more general sense, technological developments in the pumping methods and well construction have resulted in large-scale exploitation of groundwater throughout India which exceed the natural rate of replenishment of these resources. Thus, replenishment of the groundwater reservoirs by artificial recharge is essential.

TABLE 3. Water Evaporation Retardation (WER) Projects

In many parts of the country, which have to face the vagaries of the monsoon, dependance on groundwater has increased tremendously, particularly in those areas where surface water resources are either lacking or inadequate, and storage of surface water is uneconomical because of high evaporative losses. Water loss due to evaporation has led to serious problems including acute shortages of drinking water for human consumption in some parts of India. Considering the huge loss of precious water, use of Water Evaporation Retardants (WER) on open surfaces of lakes and reservoirs is now being promoted by various State Governments and Local Authorities. Various substances capable of forming mono-molecular layers on a water surface have been investigated, and fatty alcohols in their pure form were found to be most suitable and effective in retarding evaporation with no known side effects. Water savings resulting from the prevention of evaporative losses using cetyl and stearyl alcohol have been reported to be as high as 50%, but are generally between 20% and 40%. Table 3 shows a list of projects where the evaporation retardants have been used.

In India, rainfall is confined to about four months in a year and is inconsistent both in space and time, causing severe drought. In this context, whatever the source water used, irrigation is a must for agriculture in the country. However, there is an urgent need for efficient use of present available water so as to irrigate the maximum possible gross cropped area. In India, sprinkler irrigation is being adopted in hilly terrains, for irrigation of many plantation crops. The use of sprinkler systems, which mimic natural rainfalls, was introduced in the State of Hariyana in 1970, and other states like Rajasthan, Uttar Pradesh, Karnataka, Gujarat, Maharashtra have since implemented sprinkler irrigation systems. In the State of Hariyana, it has been found that, the use of sprinkler irrigation has saved about 56% of water for the winter crops of Bajra and Jawar, while for cotton it has saved 29% as compared to the traditional gravity irrigation. Drip irrigation systems, a variation on piped irrigation that delivers water directly to the root zone of the crops, are of very recent origin, and are used on a limited scale in Tamil Nadu, Karnataka, Kerala and Maharashtra mainly for irrigation of coconuts, coffee, grapes and vegetables. Experimental studies on sugarcanes, banana and other fruits have shown a very high profitability in addition to water conservation.

TABLE 4. Water Loss Under Various Irrigation Methods.

5.3 Nepal

Although Nepal has one of the world's largest per capita water resources, most of the population does not have easy access to safe drinking water and, at times, there are acute shortages of water for all economic purposes. Urban settlements are mostly affected by the shortage of water whereas, in the rural areas, the problem is linked to lack of accessibility of water. The main sources of water in the country are rivers and springs in the hilly regions, and shallow and deep groundwaters in the Terai. Due to the shortage of water from the municipal supplies in the urban settlements, primarily in the Kathmandu Valley, there is a trend toward illegal extraction of underground water using shallow and deep wells, thereby lowering the water table and leading to the possibility of land subsidence and foreseeable tectonic effects. Associated problems are the decline in the yield and productivity of wells and the increasing incremental cost of lifting water from ever-increasing depths. For these reasons, Nepal has identified freshwater augmentation technologies to protect both water quantity and water quality to the extent possible.

Alternative technologies include the use of traditional technologies such as stone spouts and Pokharis, which were the only sources of water in the Kathmandu Valley in the past. However, there is a need to conserve and restore the ponds, aquifers, wells and stone spouts which have been neglected. Conservation and restoration of stone spouts and Pokharis is related to spring development and protection. Spring protection technologies are widely used in the central and eastern hills of Nepal. These are simple and ideal technologies for use where yield of the source is very low and water is drawn at the source itself. Likewise, rainwater harvesting has been popular where there are neither springs nor streams nearby to fulfill the water demand of the community.

Various distribution systems have also been developed in Nepal based upon traditional technologies. For example, bamboo piped water supply systems are not very common, but may prove an ideal system for remote areas where GI and HDPE pipes and fittings are not available and only bamboo is easily available and cheap. Use is also being made of hydraulic rams to pump water using the hydraulic power of the water itself, thus eliminating the need for diesel or electrical power to drive water pumps. The principle advantages of this system are its simplicity and lack of an energy cost in the operation of the system. This system is suitable in places where there is plenty of water, and the area to be supplied is situated at a lower level than the source area.

5.4 Thailand

Freshwater augmentation is practised in Thailand for three main purposes; namely, for agricultural, industrial, and domestic uses. The status of freshwater augmentation technologies in Thailand is summarized in Table 5. The two most common and successful technologies are recycling of harvested rainwater in irrigation systems and rainwater harvesting for domestic rural water supply purposes. Technologies that are related to domestic rural water supply are shown in Table 6. Important issues related to the technologies are also summarized.

TABLE 5. Status of Freshwater Augmentation Technologies in Thailand.