Health aspects need to be considered during all phases of the well construction and operation. Such considerations include:
Avoiding areas of poor water quality
Shallow wells penetrate only the upper part of the groundwater body which characteristically is of the poorest quality. A check should be made on other wells in the area since this will give a good indication of the quality that can be expected in the new well. If a high salt content is suspected, a water sample from the new well should be sent to a laboratory to determine its usability for drinking. Deepening of such wells can sometimes improve quality. The deepening can be done with a small diameter tubewell in some cases or by using a reduced size concrete wall.
Proper location of the well to avoid contamination
A simple survey of past activity in the area will assist in well location. A well should not be constructed in a contaminated area. As a general rule a well for drinking should not be located within 50 metres of any contaminated areas such as livestock pens, old washing areas, sanitation facilities or heavily contaminated streams or channels. Even though such a facility has been removed from the area, it is possible that contamination will remain in the ground and continue to enter the groundwater for several years. In addition these types of facilities should not be built in the area of the completed well.
Proper well design to prevent contamination
The greatest source of well contamination is from water entering the wellhead or from water moving down the outside of the casing. Providing a watertight seal around the outside of the casing (concrete or other compacted material) is very effective in preventing movement of water around the casing. This seal should extend from the surface approximately one metre or more down. In addition providing a sloping concrete apron (or other suitable material) around the well will facilitate drainage of excess water away from the well. Facilities must also be provided to dispose of the drainage water such as percolating it some distance from the well or using it to irrigate vegetation in the area, or for cattle watering. In addition to the water-tight seal around the casing and the sloping apron around the well, the well-head should be constructed above ground level and precautions taken which prevent any drainage water or other contamination from entering the well.
Health safety precautions during well construction
Various types of contamination can occur during construction of the well and all efforts should be made to minimize these. All equipment should be cleaned prior to use in a new well since the soil on digging equipment that was used in another area is one source of contamination. Chemicals used in construction work should also be stored a safe distance away from the well. Hand-dug wells are especially susceptible to contamination from the workers. This risk can be reduced by simple, hygienic precautions during construction. Above all, defecation within the well or in the immediate vicinity of the well should be strictly prohibited.
Disinfection of the well prior to use
Even though precautions are taken during construction, all wells should be disinfected prior to use. Especially in the case of hang-dug wells, this should include scrubbing the walls of the well with a suitable disinfectant. One of the most easily obtainable and effective disinfectants is common household chlorine bleach which should be diluted 1:50 (1 part chlorine bleach to 50 parts of water) to give a chlorine solution. To provide this dilution, the volume of water in the well should be estimated and the appropriate disinfectant poured in; however, the total volume of household chlorine bleach used should not exceed 3 litres. If a pump is installed on the well the well should then be pumped for a short period of time with the pumped water returning into the well. This will disinfect the pumping equipment as well as mix the well water and disinfectant. The well should then be allowed to stand for several days (2-5 days) to allow the chlorine to dissipate. Prior to use the well should be bailed out or pumped until the smell of chlorine is faint. The remaining chlorine in the well will dissipate in a few days and cause no problems in using the well. If a disinfectant other than household chlorine bleach is used, check to ensure that it will dissipate or can be removed from the well. Many disinfectants are very effective but leave a residue which may be harmful since they were never intended to be used for drinking water or they may prove to be very difficult to remove.
Health safety precautions in operating the well
When the well has been completed, the key to its continued use as a safe drinking water source will be the user. Training the local people in simple health safeguards is the most effective control measure, although simple precautions in well design will also assist. As a general rule, no washing or cooking should be permitted in the well area and proper design of the well head can discourage this practice. Defecation or urination in the well area should be prohibited. Entering the well should also be prohibited except when required for maintenance. If this is needed, after maintenance the well should again be disinfected. Animals should not be permitted in the well area and their watering facilities should be at a safe distance. The apron around the well should be kept as clean and dry as possible to prevent mud forming around the well which can be a breeding area for hookworms and other infections. Where a pump is not used, a community bucket and rope should be provided to prevent well contamination from unsanitary buckets used to draw water. Efforts should be made to prevent this community bucket from being set on the ground where it may pick up contaminated soil which is then returned to the well on the next water draw. Where pumps are used, they should be self-priming; if not, a suitable clean water supply should be provided for priming to prevent contaminated water from being used.
The methods used to prevent contamination of a constructed well will depend strongly on the local customs and habits. A quick review of these in the light of possible contamination will prove most useful in suggesting prevention measures. Public education will be the chief mechanism in implementing these prevention measures ; however, this must be co-ordinated with an adequate maintenance programme. Without proper maintenance of the well all measures to prevent future contamination may fail. Sometimes two people are assigned each day to raise the drinking water for the small village and no-one else is allowed on the apron. This custom or some variety of it will be easily accepted if it is similar to existing habits.