Premature saturation of water demand due to rapid urbanization

Some water supply schemes in Sri Lanka very rapidly become unable to meet the demand imposed on them. This premature ‘saturation’ of the components of the water supply facilities such as intake, transmission main, treatment unit, storage reservoirs and distribution system are discussed in this paper. The reasons for it are that urbanization and industrial development are taking place at a higher rate than anticipated. As a general practice water supply schemes in Sri Lanka are designed for a 20-year life span. However most of the water schemes are saturated within a short duration. That is the 20-year design demand is reached within 4 to 5 years and the water supply infrastructure is unable to cope with the demand. This paper describes the background of these water supply schemes and causes for premature saturation. It also suggests concepts and preventive measures that can be used to overcome this problem, when designing water supply schemes in the future. The high growth in demand is a critical issue in most of the water supply schemes in Sri Lanka. Though the growth rate, migration, urbanization and industrial growth were considered, when designing the water supply schemes, the actual rate of increase in migration, urbanization and industrial growth are usually very much higher than the predicted levels. This results in them very quickly reaching their design capacity. A detail analysis was carried out of two of these schemes, to find the reasons for the problem and to propose suitable solutions. It is desirable to design a water supply scheme to cover all areas not yet likely to be developed but which are fed by the existing schemes. This is not practiced since the funds available are limited. Hence there is a tendency to limit the distribution area in order to make a scheme affordable. In the years following completion of the scheme the distribution system is often extended in all directions due to the pressure exerted on the water supply organization by the local political authority. This, coupled with the usual migration of people towards the water-served areas, leads to the premature saturation of the water supply facilities. The following optimal solution is suggested, considering all factors related to this issue. It is proposed that at the design stage all major demands are considered in consultation with all relevant institutions. The investment on the scheme can then be phased and the commissioning of the distribution areas staggered accordingly. Although it will take more time to complete the scheme in full, this will prevent the premature saturation of water schemes.