Criteria for selecting a water source

The source should be chosen so that the scheme gives the best water at the least cost and with long-term reliability. The main criteria are:

1. Quantity: The yield of the source in the driest season must meet the demand at the end of the design period, preferably with a margin. Springs and streams should be gauged in the dry season.
2. Quality: The water should be wholesome or easily treated. Sources free from pollution risk, such as springs in forested catchments, are preferred. Ground water is usually free from turbidity and bacteria.
3. Elevation and location: A source at a higher level than the town allows a gravity scheme, avoiding pumping costs. The distance from the consumers should be short.
4. Cost: Capital cost (intake, pipe, treatment, pumping) and operation and maintenance cost should be low. Compare alternatives on a life-cycle basis.
5. Reliability and sustainability: The source should not dry up or get polluted in future and should not be threatened by landslides or floods. The catchment should be protected.
6. Ownership and water rights: Legal rights of existing users, irrigation and mills should be respected; no social conflict. Permission is needed under the Water Resources Act.
7. Accessibility and safety: Site should be reachable for construction and maintenance and have good, stable foundation.
8. Environmental effect: Minimum effect on downstream users, ecology and land.
9. Future expansion: The source should permit increase in supply later.

Where several sources exist, the order of preference is usually: protected spring or gravity source, ground water, then surface water that requires treatment and pumping.