What is entailed in a water supply design?
A typical water supply system may be described as consisting of three basic components: the source of supply, the processing or treatment of the water, and the distribution of water to the end users. Water from the source is conveyed to the treatment plant by conduits or aqueducts, either by pressure or open-channel flow. Depending on the final application and water quality, water treatment may or may not be done. Following treatment, the water enters the distribution system directly or is transported to it via supply conduits.
What are the available water sources?
Water sources can be broadly divided into surface water sources and groundwater sources. The freshwater sources of Uganda include surface water (rivers, streams and swamps), ground water (deep and shallow wells, springs) open water bodies (lakes) and rainfall.
Why is water source important for design?
The selection of a source of supply will be based on water availability, adequacy, quality, cost of development and operation and the expected life of the project to be served. The selection of a suitable source or combination of sources of water is one of the initial steps in designing a water supply scheme. The source or sources of water must be capable of supplying sufficient water of acceptable quality for the application or end user. Sources which require little or no treatment of raw water such as springs, wells and boreholes should be given the highest selection priority provided their yields are sufficient to meet the water demands of the end user or final application. In selecting surface water sources, rivers with upland mostly forested catchments should be given preference.
How does water source drive cost of water supply system?
Small water systems are often supplied from groundwater or from perennial protected springs. Because of its inherent characteristics, ground water in rural areas is quite often considered as safe enough to be provided directly without treatment i.e. with a hand-pump. Costs are relatively lower than with other forms of supply, which makes it a popular choice with service providers.
Where there is no other option than to use surface water, construction of impoundments in rivers and streams is mostly required to provide a continuous supply of raw water throughout the year for treatment and distribution. The costs of creating an impoundment in a small water supply system can be a considerable proportion of the whole system cost.
The capital cost of groundwater sourcing are two-fold; the direct costs of gaining access to an aquifer either by drilling a borehole or digging as well, and the cost of lining such a borehole or well where the well has to penetrate soft material in the earth. A good estimate of drill-well costs can be made, for example, by using unit rates for linear metres of hole drilled and lined, respectively. The unit cost here is usually capital cost per meter drilled including the final finishing of the well such as casing and concrete surface collar – depending on the extent of the service rendered by the drilling company. The final capital cost will therefore depend on the depth of the drill-well.
The maintenance cost will be a percentage of the civil structure. Operation costs will be minimal on the well itself if the well was properly installed. Also if the pumping system is driven by solar power using solar panels, the initial costs are slightly high but the maintenance costs over the long run are significantly low to zero. The pay-back period of initial investment of solar powered pumping is about 2-3 years. A good solar powered pumping system will work for up to 15 -20 years if the water source remains sufficient.