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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