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Water use efficiency

In distinguishing among the three major water using sectors--agriculture, industry and domestic--the difference between consumptive and non-consumptive water uses is often neglected and the concepts are often misused. Unlike most resources, water can be used repeatedly at different times and locations. The following examples may help to distinguish between the two.

• Examples of consumptive uses are: evaporation losses from reservoirs and during crop irrigation; evapotranspiration through plants and vegetation in agriculture and green urban areas; evaporation from cooling processes and water used in industrial products (e.g. soft drinks and food processing); and the drinking of water.

• Examples of non-consumptive uses are: hydropower generation; recreation; fishing; navigation; washing processes in industry; and cleaning in domestic uses.

• Changes in water quality, such as the concentration of pollutants, temperature and salinity level, affect water availability. Therefore, water quality deterioration during non-consumptive use reduces the availability of water for consumptive uses.

• Water losses through soil percolation and seepage in agriculture, or in urban environmental uses such as public parks and gardening, and maintaining flows in streams, can be classified in either group. It depends upon whether the water lost in one use is reused somewhere else.

 

 

What efficiency are we talking about?

The word 'efficiency' relates outputs to inputs, and has different meanings in different contexts. In economics, efficiency usually relates financial (or adjusted financial) returns from water use to the cost of water supplies. In agronomy, efficiency relates the ratio of the volume of goods produced to the amount of water consumed.

In this paper, the concept under discussion is technical water use efficiency. It is the relationship between the amount of water required for a particular purpose and the quantity of water delivered. It is an important measure to guide conservation efforts for water resources. In addition, the effectiveness of water delivery can be another measure to evaluate the timeliness of supply, quantity, equity in allocation, and the quality of water. However, this concept of effectiveness is not covered in this paper.

The technical efficiency criterion can be applied to different levels of water use, depending on how physical boundaries are defined. For instance, it can refer to a distribution system, a manufacturing enterprise, a field or an individual farm, a project area, a basin, or a sector. Debates about 'water use efficiency' are often based on an inadequate understanding and inconsistent use of the term 'efficiency'. In some cases, this confusion has led to faulty investment strategies, policies and actions.

The next section reviews the definitions of water use efficiency at various levels within different sectors. It then uses examples to illustrate the issues that are involved in evaluating WUE.

 

 

What are current levels of water use efficiency in irrigation?

DEFINITIONS. In irrigation, the delivery of water from water sources to field crops depends on the efficiency in three main levels of an irrigation system: conveyance, distribution, and field (on farm) application (Bos: 1983; 1990). Figure 1 illustrates the framework of analysis for a typical irrigation system.


Figure 1 An Irrigation Framework

i. Conveyance is the movement of water from its sources (reservoirs, river diversions, wells or pumping stations) through main and secondary canals to the tertiary offtake of a distribution system. Conveyance efficiency, Ec, is defined as:

Ec = Vd/Vs. where: Vs = volume diverted from sources plus inflows to the canal from other sources; Vd = volume delivered to the distribution system.

ii. Distribution is the movement of water from tertiary and distribution canals, channels or pipes to individual field inlets. Distribution efficiency, Ed, is defined as:

Ed = Vf/Vd. where: Vf = volume furnished to the field.

Often, the combined efficiency of a conveyance and distribution system is described as irrigation network efficiency, En. It is defined as the water delivered to farm field inlets divided by the water diverted from the prime source:

En = Vf/Vs = Ec x Ed.

iii. Field application is the movement of water from field inlets to crops. The field (or on-farm) efficiency, Ef, is defined as:

Ef = Vm/Vf. where: Vm = net volume needed to maintain the soil moisture, which is equal to the amount consumptively needed for evapo-transpiration, i.e. Vm = (crop water requirement) - (effective rainfall).

Another concept widely used in irrigation is the overall or project efficiency, Eo. It is the ratio between the quantity of water consumptively used by crops and the total water diverted from the sources to a project area. It encompasses seepage and evaporation losses incurred in physically conveying water to crops, as well as losses due to deep percolation through the root zone to groundwater and field runoff.

Eo = Vm/Vs = Ef x Ec x Ed.

Finally, irrigation sector efficiency, Ei, is defined as the amount of water actually consumed by the sector divided by the amount of water made available for the sector of a country.

EXAMPLES. Examples of WUE at different levels and project areas in selected countries are presented in Table 3 (a, b, c, d), incorporating data from several sources. Later sections of this paper present a detailed analysis of the figures in Table 3. An overview comparing water use efficiencies between the developing countries and the United States is presented below

On average, the network efficiency, En, for developing countries has been estimated at 68 percent. Most countries show a range of 60-75 percent. The average En in the United States is estimated at 78 percent. According to the sources reviewed for this study, the on-farm efficiency, Ef, varies from 40-85 percent. In the United States, the Ef in the intensively developed areas ranges from 50-85 percent, with a national average of 53 percent. The average Ef in developing countries is around 40 percent. The overall efficiency Eo, encompasses losses from conveyance, distribution and field application, and therefore varies widely. The Eo of many systems can be as low as 20 percent, such as in Yemen. Well-managed systems show efficiencies of 50 percent or more, such as in Cyprus. The average for developing countries is 30 percent. For pipe delivery systems in the United States, Eo varies from 30-80 percent, with a national average of 41 percent. Most cases cited in Table 3 show an Eo of less than 40 percent, except for Cyprus, Jordan and the two project areas in Doukkala in Morocco. All three cases, which have Eo values of more than 40 percent, reflect the impact of sprinkler, drip and advanced water control technologies. In Cyprus, for example, all irrigation water supplies in the public irrigation systems as well as all groundwater extractions are metered. This accounts for the high efficiency level. There is suggestive evidence that an overall efficiency of 45-55 percent may be a ceiling for a gravity system in the cultivation of non-paddy crops.

Table 3 Irrigation Water Use Efficiencies at Various Levels

Table 3a Network Level

Countrv

(%)

Specification

Cyprus

95

Pipe conveyance systems with sprinkler and drip

U.S.

78

Average

France

75-85

Bas-Rhone region, main canal 100% lined

Jordan

75

Open canals with manual control, on-farm sprinkler/drip storage &

Morocco

74

Doukkala project with sprinkler system

Morocco

72

Doukkala project with gravity system

Morocco

70

Open canal systems with hydraulic irrigation control & surface

West Bank & Gaza

74

Ec=87%, Ed=80-90% for distribution wells system of artesian

Dev.g countries

68

Average

Egypt

67

Ec=75 % and Ed=89%b

Mexico

67

Sinaloa project

Colombia

65

Coello project.

Mexico

61

Yaqui project.

Syria

60

Most schemes at 60% with upper limit of 75%b

Turkey

60

Traditional open canal systems with manual controld

Kyrghyzstan

55

poor cosign, built and maintenance of distribution canals'

Mexico

54

Panuco project

Yemen

50

Large-scale spate irrigationd

Pakistan

45-60

Ec=75% and Ed=60-80%b

Table 3b On-farm Level

Country

(%)

Specification

East India

85

Rico irrigation on shallow soils over hard-rock areas.

Israel

75-80

nearly 100% by sprinkler irrigationb

Cyprus

70

Pipe conveyance systems with sprinkler and dripd

Jordan

70

Open canals with manual control, on-farm storage & sprinkler/dripd

Morocco

67

Doukkala project with sprinkler systema

Morocco

60

Open canal gravity systems with hydraulic control & irrigationd surface

Morocco

58

Doukkala project with gravity system

Mexico

55

Both Yaqui and Sinaloa projects

U. S.

53

50-85% in intensively developed areasc

Turkey

50

Traditional open canal gravity systems with manual controld

Syria

50

Basin irrigation method usedb

Kyrghyzstan

50-60

15% by sprinkler system

Mexico

48

Panuco project

Colombia

45

Coello project

Yemen

40

Large-scale gravity irrigation on the farmd

Dev.g countries

40

Averagec

 

Table 3c Overall Level

Country

(%)

Specification

Cyprus

66

Pipe conveyance systems with sprinkler and dripd

Jordan

53

Open canals with manual control, on-farm storage & sprinker/dripd

Morocco

49

Doukkala project with sprinkler systema

Morocco

42

Doukkala project with gravity systema

Morocco

42

Open canal gravity systems with hydraulic control & surface irrigationd

Kyrgbyzstan

40-45

small stream reservoirs recapture part of drainage flow in Chu Valley, plus 10% groundwater usec

U.S.

41

Averagec

Mexico

37

Sinaloa project

Philippines

36

Upper Pampanga and Aurora projectsa

Mexico

34

Yaqui project

Turkey

30

Traditional open canal gravity systems with manual controld

Syria

30

b

Dev.g countries

30

Average.

Colombia

30

Coello project

Thailand

28

Two Lam Pao areas with hip rainfall, low crop intensity in dry seasons!

Mexico

26

Panuco project

Yemen

20

Large-scale gravity spate irrigationd

 

Table 3d Sector Level

Country

(%)

Specification

Egypt

89

Nile basin estimate

U.S.

87

Based on data from 17 Western States of U.S.

Israel

80

b

Ethiopia

60-80

b

Syria

60

Average

Jordan

42

38 % for surface distribution and 70% for direct pipe distribution

 

Sources:

a), b), c) and d) are reference sources referred before (see footnote 1); f) Le Moigne, 1992b

There is kale data available on sector efficiency (Ei). In the United States, Ei has been estimated at 87 percent. Two reasons contribute to the high rate: i) the repeated use of water in different activities in a basin, or in several basins after inter-basin transfers take place, that results in improved efficiency. For example, in the seventeen Western States, 46 percent of irrigation waters are reused (Frederiksen, 1992). ii) intensive use of high irrigation technology. More than 40 percent of the irrigation lands are equipped with sprinkler systems and 3 percent with drip systems. Both systems use water more efficiently than other commonly used techniques. By contrast, the irrigation sector efficiency in Syria is 60 percent. The current flood irrigation method is the main cause of a low Ei. Water losses of 50 percent are common for such methods. Detailed analyses on Israel, Egypt and Jordan will be presented in the later sections of this paper.

 

 

Factors affecting irrigation water use efficiency

Many factors affect WUE in the irrigation sector. They include seepage, percolation, soil depth and texture, evaporation and evapo-transpiration, design of irrigation structures and their operation and maintenance, and management skills. At various efficiency levels, climate and rainfall patterns, size of irrigated areas, and methods of water application also play important roles.

SEEPAGE AND PERCOLATION losses reflect irrigation water losses from unlined and poorly lined distribution canals, ditches, and from crop fields. In the Bas-Rhone region of France, main canals are entirely lined and well maintained. This results in a high network efficiency of 75-85 percent. In Pakistan, losses in conveyance systems are high. About 25 percent of the supplies diverted from rivers is lost in the canal system through seepage and evaporation before it reaches distribution inlets. From the inlets, losses through secondary watercourses have been measured at 2040 percent. As a result, only 45-60 percent of the supplies diverted from rivers is actually delivered to the fields (Murk, 1991). In Kyrghyzstan, seepage and leakage losses in the distribution system are also considerable. Only 24 percent of the canals are lined, resulting in a network efficiency of 55 percent (Le Moigne, 1992b). Seepage losses are sometimes reused elsewhere in the basin. This aspect will be discussed in Chapter V.

SOIL DEPTH AND TEXTURE can make a significant difference in efficiency levels. Two extreme examples are the Gezira scheme (Sudan) and East India. The Gezira irrigation system has an extremely high network efficiency of 93 percent (Plusquellec, 1990). Although the design of the minor canals is a contributing factor, the high efficiency is due mainly to the nature of the soil. The soil is highly impermeable and significantly reduces leakages from the system. These factors account for an overall efficiency level of 70 percent. In some areas in East India, soils are shallow and rice irrigation is performed over hard-rock areas. These effectively prevent water losses and lead to high field efficiency levels of about 85 percent (Frederiksen, 1992). Frederiksen's study also shows that water applications needed for rice production on heavy clay soils can be only a quarter of those on light textured soils. Canals passing through coarse materials, common in alluvial fans, can lose huge quantities of water.

EVAPORATION AND EVAPO-TRANSPIRATION losses are associated with open canals, irrigated fields and crop growth. In Egypt, the annual evaporation losses from irrigation canals are estimated at 2 billion m³ (Abu Zeid, 1991). In Jordan, the high evaporation rates and seepage losses from open irrigation canals in the Jordan Valley are one of the main causes of water losses of up to 58 percent in the agricultural sector (Abu Taleb, 1991). The study by Abu Taleb shows that, if these losses are effectively reduced, the quantity of water savings could reach 50 million m³ per year. Cyprus has a high network efficiency of 95 percent (Van Tuijl, 1992), due to complete pipe conveyance systems distributing water to the sprinkler and drip irrigated fields. The average on-farm efficiency is estimated at 70 percent, and overall efficiency 66 percent. The systems have successfully prevented losses from both seepage and evaporation.

FAILURES IN DESIGN OF IRRIGATION STRUCTURES contribute greatly to inefficient water use. Many systems were designed to meet only limited objectives, and are not suitable for modern agricultural practices. Technical constraints to these systems often limit the possibility for improvement through better management, such as in some areas of Ethiopia (Abate, 1991), where many canals in the small districts in the highland areas are unprotected against erosion. The headworks of canals are often washed away when floods occur.

Poor land leveling has been a constraint to proper on-farm water management. For instance, many areas in Upper Egypt that were converted to perennial irrigation after construction of the Aswan High Dam are not properly leveled. Fragmented land and small and separate holdings limit establishing efficient irrigation methods. Surface irrigation systems are used in most cultivated lands of the Nile Valley. The overall water use efficiency of individual farms is generally low. Farmers apply excessive irrigation water to reach areas at higher elevations. As a result, water which is not consumed by plants infiltrates and recharges groundwater or flows into the drainage system (Abu Zeid, 1991). Although downstream users along the Nile reuse a large part of the drained water, excess irrigation water leads to salinity problems by raising groundwater tables.

The main cause of high water losses in the irrigation systems of Kyrghyzstan is the poorly designed structure of distribution canals (Le Moigne, 1992b). As a result, the facilities for water control are underdeveloped. Most gates, manually operated, do not function because of poor maintenance and vandalism. Joints between units are often missing. By contrast, the main canals-particularly those downstream of large storage dams--are better designed and more advanced, with remote monitoring and automatic control. Maintenance of the equipment is of a high standard. Clearly, the appropriate design of irrigation systems is a prerequisite for effective operations and management.

LACK OF WATER CONTROL DURING NIGHT AND WEEKEND IRRIGATION is another problem in many developing countries. The study by Abu Zeid (1991) shows that, in Egypt, the average conveyance losses between main canal intakes and distribution outlets was 25 percent. That between the distribution outlets and fields was 11 percent. The combined effect leads to a network efficiency of 67 percent. The main reason for these losses was that farmers abstained from night irrigation. Irrigation networks were designed to operate for 24 hours a day. Thus, considerable amounts of water were drained wastefully at night, when irrigation was not practiced. As a result, some farmers faced water shortages during the day. A conservative estimate for Ethiopia shows that it is possible to increase the current irrigated area by 20-40 percent by reducing irrigation water losses during nights and weekends (Abate, 1991). In Sudan, the original design and operational concept of the Gezira scheme adopted night storage systems (Plusquellec, 1990). By adjusting water releases at the headworks according to demand, it was possible to reduce excessive water losses. Due to various reasons (see following section), the night storage system was not used for a period of time. It was re-introduced by the Government after revising the design of the minor canals (Zaki, 1991). The new system not only reduces operational water losses, but also reduces siltation in the minor canals downstream.

WEAKNESSES IN MANAGEMENT means poor implementation of water control regulations and operation rules, and inadequate maintenance. It is an important factor explaining water losses in the irrigation sector. Inadequate O&M has caused severe deterioration of irrigation canals in many countries. The two Lam Pao projects in Thailand are examples of losses due to poor maintenance of irrigation diversion structures (QED, 1990). The two projects showed lower than expected efficiencies (28 percent instead of the 55-58 percent estimated at appraisal). The main reason for water losses is seepage from the main canals. Although the canals were lined, cracks and breakages occurred all over the canal linings because of failures in maintenance and inadequate weed cleaning in the tertiary system. As a result, there was little difference in seepage losses between lined and unlined canals. The same is true for some project areas in the Philippines (AST, 1991). In Egypt, for nearly 25 percent of existing canals, the actual widths exceed the design widths due to degradation and the misuse of canal banks. This has consequently changed water levels and canal discharges (Abu Zeid, 1991).

The regulations for managing water systems are often inadequately designed to meet variable supplies and demands. In Sudan, for instance, irrigation management operates on the basis of 'upstream control'. The Ministry of Irrigation controls the delivery of water to the heads of minor canals. From there on, field inspectors have the responsibility for supervising the rotational delivery of water to the fields. Farmers or farmer organizations handle the on-farm water management. This division of responsibility has been problematic. Farming programs, which determine crops, cropped area, rotation and cropping intensity, often have not been reflected adequately in the water delivery programs (Zaki, 1991).

CLIMATE PATTERNS AND EFFECTIVE RAINFALL affect irrigation water use efficiency. Reviewing previous definitions, the actual irrigation requirement, Vm, is the crop water requirement minus effective rainfall. Under-irrigation or over-irrigation in different seasons artificially affects efficiency levels.

The Philippines Upper Pampanga River Integrated Irrigation System (UPRIIS) is a typical example. Table 4 shows the overall efficiency, Eo, during both seasons for three continuous years. Eo is higher in the dry season. In the wet season, Eo is low due to high rainfall. There were apparently not enough incentives for farmers to save excess water from the run-ofriver system. In fact, project staff reported that during wet seasons farmers complained more often about flooding from uncontrolled river flows and high rainfall of all than about water shortages. The low efficiency level of 20-30 percent reflected more the virtual absence of a need to use river flows and rainfall effectively, than the actual technical inefficiency in the system. Underirrigation during dry seasons also artificially increased efficiencies.

Table 4 Overall Efficiency for Two Seasons (Philippine UPRIIS projects)

 

1986

1987

1988

Wet season

23.3

32.5

28.0

Dry season

54.6

46.9

52.0

Source: OED report, 1990

A similar phenomenon has been seen in areas of Lam Pao in Thailand and in the Panuco basin in Mexico (QED, 1990). In some project areas, high rainfall occurs in the wet season and low cropping intensity is practiced during dry seasons. The average overall irrigation efficiencies in those areas is below 30 percent. In Thailand, the estimated overall irrigation efficiency varied widely, from 8-51 percent in the wet season, and from 17-70 percent in the dry season (Vadhanaphuti, 1991), depending on the physical condition of the infrastructure and the availability of water.

Under these circumstances, a distinction should be made between water diverted and water pumped or released from reservoirs. If water is released at the expense of a storage or reservoir, pumping costs and delivery operations, it will affect the operational efficiency of these facilities. Will surplus water cause problems of drainage, flooding, water logging, and salinity in downstream areas? Alternative indicators need to be used to measure water use efficiency in such cases.

METHODS OF WATER APPLICATION are an integral part of optimal water use. There are many references on WUE levels under different application methods. Syria is an example where the technique of basin (flood) irrigation is widely practiced. This method can cause water losses of more than 50 percent (Bakour, 1991). Irrigation network efficiencies are 60 percent in most of the agricultural schemes of the country. Of the total water use of currently 10.3 billion m³ in the agricultural sector, more than 4 billion m³ is lost every year. Excessive irrigation without well-designed drainage networks causes a rise in groundwater levels, leading to increased salinity and lower agricultural productivity. In Yemen, the spate irrigation method is widely practiced. According to a study by Van Tuijl (1992), the overall WUE is 20 percent, much lower than the developing country average. Although spate irrigation has a low efficiency, it is a commonly practiced method to economically capture flood waters for irrigation. It also recharges the groundwater aquifer, from which the water is pumped for reuse in irrigation.

 

 

Water use efficiency in the urban sector: Definitions

DEFINITIONS. Urban water use encompasses both industrial and domestic activities. The latter includes residential and commercial (services, office buildings, and public parks) uses. Figure 2 illustrates a typical urban water supply system. Similar to the descriptions used in irrigation, conveyance efficiency, Ec, in this setting is defined for systems between water sources and water treatment centers. Distribution efficiency, Ed, which is the main indicator of the overall effectiveness and operation and maintenance performance of an urban water supply system (usually in pipes), is defined for systems between treatment centers and end-users (households, factories, public standbys),

Ed = Vd/Vs


Figure 2 Urban Water Supply System

In urban water supply projects, one common measure of Ed is through use of an indicator called unaccounted-for water (UFW), i.e. UFW = Vs - Vd (see Figure 3), therefore,

Ed = (Vs-UFTY)/Vs = 1-UFWr


Figure 3 Losses and Illegal Water Use

where: UFWr = UFW/Vs, standing for the ratio of unaccounted-for water.

However, there seem to be different ways of defining Vd in urban sector water use, which has led to the inconsistent use of the term, UFW. Here are some examples from Bank documents.

• The Bank's Working Guidelines on 'The Reduction and Control of Unaccounted-for Water', prepared by the INU Department Jeffcoate, 1987), defines UFW as the difference between the volume of water delivered into a supply system, Vs. and the volume of water accounted for by legitimate consumption, Vd, whether metered or not. As illustrated in Figure 3, by this description UFW consists of two parts: i) physical leakages from distribution pipelines, house connections, valves, and hydrants; and ii) illegal connections (non-physical losses). Since un-metered water is not necessarily lost, legitimate consumption, Vd, includes the amount of water metered, intentionally un-metered for public uses (such as fire service, street cleaning, construction, and public buildings), and the amount of water unrecorded due to meter damage and lapses in reading.

• However, there seems to be some ambiguity about including un-metered public water uses as part of unaccounted-for water. The Working Guidelines also state that the UFW includes "water consumed but not recorded by consumer's meters or otherwise accounted for by government/public use".

• A Planning Manual published by the Bank (Okun, 1987) defines UFW as the difference between the measured produced water and the metered water used.

• A recent OED report (1992) defines UFW as 'the difference between the measured volume of water input into a system and the amount of water sold'.

This inconsistency in the definition of unaccounted-for water may lead to non-comparable evaluations of efficiencies in urban water supply projects. A generally agreed definition would avoid such problems.

Unlike the field efficiency in irrigation, end-user efficiencies in the urban sector are classified into: industrial consumptive use, Eic; domestic consumptive use, Edc; and overall urban sector use, Eu. Figure 4 illustrates the concepts with simple numerical examples. Consumptive use of water in industry includes evaporation losses (such as cooling processes in thermal, steel and manufacturing industries), the amount used in products (such as food processing and beverage industries), and unaccounted-for losses (such as leakage). Although the leakage losses should be differentiated from consumptive uses, it is usually difficult to separate them out because the estimate of consumptive water use is usually obtained from the amount of water supplied less the amount discharged into the sewers or rivers.

 

 

Factors affecting urban water use efficiency: Examples

Table 5 presents some statistical data on the distribution network efficiency of urban water supply systems in several countries. Israel has the highest efficiency of 87 percent, or 13 percent for unaccountedfor water (Schwarz, 1991). This can be attributed largely to the highly flexible and integrated national water supply system, the National Water Carrier. The Carrier distributes about 2,000 million m³ of water annually. Because the system is energy-intensive, the unit cost of water supply is high. The costs vary from US$0.03/m3 at low lifts with short distance conveyance schemes, to US$0.501m3 at high lifts with long distance conveyance schemes, and reach US$4/m³ for desalinated water. These high costs of water production provide strong motivation for efforts to achieve a high level of efficiency. In the United States, distribution efficiency is also high, around 83-88 percent, or UFWr at 12-17 percent (Frederiksen, 1992). The main reasons are the highly developed distribution networks and metering systems. By contrast, high levels of UFW of up to 50 percent are common in many developing countries (e.g., Turkey and Egypt). The network efficiency of the urban sector in many developing countries ranges between 50-75 percent.

Poor operation and maintenance of supply facilities cause leakages in supply systems. The inappropriate implementation of regulations, failure to meter and illegal tapping are also causes for inefficiencies in the urban water sector.

LEAKAGE is a critical problem in urban water supply. It accounts for a large part of water losses, especially in areas where metering regulations are weak. Old or poorly constructed pipelines, inadequate corrosion protection, poorly maintained valves and mechanical damage major contributing factors. One effect of water leakage, besides the loss of water resources, is the reduction in pressure in the supply system. Raising pressure to make up for such losses increases energy consumption. Not only does that make leaking worse, it also has adverse environmental impacts.


Figure 4 Water Use, Reuse and Consumption in Urban Systems

 

 

 

Studies carried out by the Addis Ababa Water and Sewerage Authority in Ethiopia (Abate, 1991) show that leakages from the urban distribution system could reach 30 percent. In Turkey, in most municipalities, water leakages in the distribution network have reached levels that are far from acceptable (Bilen, 1991). Urban water supply losses in Ankara and Istanbul were estimated at 50 percent in 1990. The main reason was inadequate renewal and maintenance of the system. Interruptions in water delivery were usual. Many cities in Sudan experience considerable losses of water supplies. The average water losses were estimated at 25 percent (Table 6). These figures are relatively low compared with other developing countries. They are, however, costly, especially when there are serious shortages of water in the country. In some countries of the Nile basin, urban water losses are almost twice as high. In Egypt, urban domestic water use was 3.1 billion m³ in 1990. Distribution losses were 50 percent (Abu Zeid, 1991). The country is planning to maintain the present level of domestic water use in the year 2000 (with an increase of 14 million people), mainly by reducing losses from 50 percent to 20 percent.

WATER METERING is still inadequate in many towns and cities. Users are charged a flat fee no matter how much water they consume. Illegal tapping and un-metered public uses are more significant in areas where there is metering but regulations are not adequately enforced. The inefficiencies result partly from large government subsidies that vary among users. Even where metering is carried out, inadequate testing, meter reading and maintenance continue to be severe problems in many countries. For example, in Jordan, the municipal supply systems serve more than 440,000 recorded residential, commercial and light industrial users. The urban demand in 1990 was 210 million m³, with per capita water use of 190 1/day. The losses in the municipal and industrial sectors were 25 percent (Abu Taleb, 1991), due to aging pressure pipes and inaccurate meters. The illegal diversion of water to bypass meters was significant. If the losses can be reduced to 15 percent, for example, by investing in the rehabilitation of supply networks, potential water savings are estimated at 100 million m³ per year.

Table 5 Urban Water Distribution Network Efficiency (%)

Country

Effi.

UFW

Note

Israel

87

13

1990 data

United States

83-88

12-17

1984 data.

Jordan

75

25

1990 data

Sudan

75-77

23-25

most cities

Ethiopia

70

30

Addis Ababa

Turkey

50

50

Ankara, Istanbul, 1990

Egypt

50

50

1990 data

Devig. country

50-75

25-50

average

Sources: Le Moigne, et.al. 1992a; a) Frederiksen, 1992

 

Studies by Okun (1987) show that, in general, a 10-20 percent allowance for unaccounted for water is normal. But a ratio of more than 20 percent requires priority attention and corrective actions. A review of 54 Bankfinanced water supply and sanitation projects found that the average ratio of unaccounted-for water was 34 percent (Jeffcoate, 1987). The recent Bank review of 120 urban water supply and sanitation project completion reports identifies unaccounted-for water as a severe problem in urban water supply projects. This problem requires substantial corrective investment (QED, 1992).

THE EFFICIENCY OF CONSUMPTIVE WATER USES in the domestic and industry sectors is usually affected by technologies used in the production processes, structure of industry, and the style of living and standards of urban households. Pricing policies also play a role at this level.

A study by Frederiksen (1992) shows that, in the United States, the efficiency of consumptive water use, Eic, in industry as a whole is 16 percent and that of thermal power generation is 3 percent. In Beijing (China), the Eic is estimated at 29 percent (Xie, 1986). As water becomes scarcer, the development of new technologies in industrial processes has to be directed towards producing more goods with less water. Efficiency of domestic consumptive water use, Edc, in developing countries is estimated at 35-85 percent, with a per capita water use of 15 40 l/day (Frederiksen, 1992). This efficiency level is higher than in some industrialized country cities, whose average Edc is 10-20 percent with per capita water use at 350-600/day. The explanation for low urban sector efficiency levels in the developed countries may lie in the style and higher standards of living. For example, developed countries use more water to water public parks, green areas, yards and gardens, in environment and recreation, and in residences for water appliances.

Table 6: Urban Water Losses (Sudan, 1990) m³

Region

Demand

Losses

(%)

Khartoum

250,000

62,500

25.0

Eastern

41,250

10,200

24.7

Northern

21,860

5,400

25.0

Darfur

6,800

1,700

25.0

Kordofan

22,700

5,500

24.0

Central

67,560

16,000

23.8

Total

410,170

101,300

24.6

Source: Zaki, 1991