C. Water

a. Freshwater Sources

Fresh water comes from three main sources: surface water (streams, rivers, lakes), ground water (underground or emerging from springs), and rainwater.

(1) Surface Water

Surface water is collected directly from streams, rivers, lakes, dam outflows, reservoirs, and ponds. Where such a source holds water year-round, the water table in the vicinity can be expected to be near the surface. Surface water should always be considered microbiologically unsafe unless proven otherwise and therefore is likely to require treatment measures before it can be used. Direct access may also cause difficulties with the local population. Using ground water that has passed through the natural filter of the soil is preferable to collecting surface water. If the soil is not sufficiently permeable to allow extraction of sufficient quantities of water from shallow wells, bore-holes, or springs, however, surface water may be the only option. In such circumstances, emergency treatment measures such as storage, sand filtration, and chlorination are advised. Control of access to surface water is essential.

(2) Ground Water

Springs are excellent sources of ground water. Spring water is often safe at the source and can be piped to storage and distribution points. Spring water should be collected above the camp, if possible. Care should be taken to check the origin of spring water, as some springs may be nothing more than surface water that has seeped or flowed into the ground a short distance away. The source, or the point at which the spring water flows to the surface, must be protected against pollution. A simple structure of stone or concrete should be constructed at the source to allow the water to flow freely from a pipe into a tank or other collection vessel. Care must also be taken to prevent contamination in the catchment area above the source. The quantity of water supplied from a spring may vary widely with the seasons, with minimum flows occurring at the end of the dry season.

Another desirable option is to supply ground water by means of drilled boreholes or hand-dug wells. Ground water, being naturally filtered as it flows underground, is usually microbiologically pure unless polluted surface water has infiltrated the supply. The choice of method to raise ground water will depend on the depth to the water table, yield, soil conditions, and availability of expertise and equipment. Table III-3 and figure III-1 provide additional information on several methods of digging or drilling wells.

Even though wells are often used to access ground water, they have several disadvantages. Without good ground water surveys, preliminary test drilling, or clear local evidence from nearby existing wells, no guarantee warrants that new wells will yield adequate supplies of good quality water. Drilling or digging wells can also be expensive. A hydrogeological survey must be undertaken before starting any extensive drilling program. For these and other reasons, attempting to improve or rehabilitate an existing well is sometimes better than constructing a new one.

Drilled boreholes, hand-dug wells, and pumps must be disinfected immediately after construction, repair, or installation of equipment, as they normally become contaminated during the improvement work. In addition, boreholes and wells must also be protected from pollution. Open wells are especially vulnerable to contamination caused by surface water inflow and unsanitary ropes and buckets. Wells should be protected through the installation of a hand pump if feasible. Wells and boreholes should be constructed so that surface water, seasonal rain, or flood water will drain away from the wellhead. Wellheads should be located above and at least 30 to 50 meters away from any sanitation facilities and their discharges.

(3) Rainwater

Rainwater may be a primary source of water in areas with adequate and reliable rainfall. Reasonably pure rain water can be collected from the roofs of buildings or tents if they are clean and constructed of suitable materials. Rainwater collection, however, is not always reliable and requires large rooftop areas as well as individual household storage facilities, making it generally impractical for many DP emergencies. Nevertheless, every effort should be made to collect rainwater. Small collection systems using local earthenware pots under individual roofs and gutters, for example, should be encouraged. Allow the first rain after a long dry spell to run off; this washes away the accumulations of dust, sediment, and bird droppings.

b. Seawater

Seawater can be used for almost everything but drinking and cooking, thus reducing freshwater requirements.

c. Water Source Considerations

Consider the following when selecting an appropriate water source:

• Volume of supply.
• Reliability of supply (taking into account seasonal variations and extraction methods).
• Water purity, risk of contamination, and ease of required treatment.
• Speed with which the source can be made operational.
• Rights and welfare of local population.
• Appropriate technology and ease of maintenance.
• Cost.

Table III-3. Characteristics of Different Types of Well Construction

Note: The yield potential of a well depends on the geological formation where the well is positioned, the contours and gradients of the land, and the well construction. Up to the limits of the aquifer’s safe yield, actualoutput depends on the pump. If wells are sited too close together, yields will be reduced. If too many wells aredeveloped in a given area, long-term yields of the aquifer may be adversely impacted.

Figure III-1.

Figure III-1 Methods of Well Construction

TOC: C. Water