Cleaning and disinfecting wells
Technical note 1 on drinking-water, sanitation and hygiene in emergencies
Step 1: Inventory of wells
Flooding, earthquakes, civil unrest and other natural and man-made disasters often cause damage to hand-dug wells. This technical note sets out the actions needed to repair and rehabilitate a hand-dug well so that it can be returned to its former condition. The emergency repair and rehabilitation measures proposed are temporary and should be followed by measures for permanent rehabilitation.
Steps for cleaning and disinfection
Figure 1.1 outlines a four-step approach to cleaning and disinfecting wells after natural or man-made disasters. It is an emergency approach designed to rehabilitate wells so that they produce water of a similar quality to that supplied before the disaster (see Box 1.1). Technical note 15 gives further information on wells contaminated by seawater.
Step 1: Inventory of existing wells
The disaster may have contaminated or damaged a large number of wells. The first step must be to select which wells should be repaired first. They are the ones that are used most and that are easiest to repair. The following actions should help you to make an informed selection:
- Meet with community leaders and ask them which wells serve each section of the community.
- Select the most commonly used wells as a source for drinking- water that provided a plentiful supply.
- Check there are no obvious sources of contamination from nearby latrines, ponds or surface water. Also map livestock areas (pig pens, cattle sheds, chicken coops) as potential sources of contamination by animal waste.
- Assess the type and extent of damage to the top of the well and the lining.
- Ask the community about the original depth of the well. Use this to estimate the amount of silt and debris in the well.
- Test the pump (if there is one) to see if it is still working. If not, determine the repairs necessary.
- Estimate the resources needed for repairs (personnel, equipment, time and materials).
Figure 1.1: Steps for cleaning and disinfecting wells
Step 1: Produce an inventory of existing wells
Step 2: Clean and rehabilitate the wells
Question: Test turbidity levels. Are they less than 20NTU? If no, go to Step 2. If yes, go to Step 3
Step 3: Disinfect the wells
Step 4: Dewater the wells and monitor chlorine levels
Box 1.1: Water quality from hand-dug wells
Water taken from hand-dug wells is often of poor quality, mainly due to the poor construction of the above-ground elements and unhygienic methods of collecting water. The steps described here will not overcome these problems as they are designed to return the well to its original condition.