Protect a well against contamination with four things: a site at least 30 m from any latrine, animal pen or waste and uphill of them, a watertight seal on the upper 3 m of the lining or the hole, a concrete apron 3 m across that slopes away from the wellhead, and a cover over the opening. A well is a direct pipe from the surface to the aquifer, so any one of these missing lets surface water short-circuit into the drinking water.
Part of Deep Wells
Well protection is the set of structures and siting rules that keep surface water, animals and waste out of a well. It matters as much as the digging, because a well that yields plenty of dirty water is worse than none.
Groundwater Is Clean Only If The Surface Cannot Reach It
Soil and rock filter water as it soaks down, so groundwater is usually cleaner than a stream. A well breaks that protection: it is a hole through the filter. Rain and spilled water that run into the opening, down the outside of the casing, or through a cracked lining go straight to the aquifer with none of the filtering. Contamination reaching a well by this surface short-circuit is a common cause of well-borne illness, and unlike the aquifer it is entirely in the builder’s control.
Four Barriers, Each Covering A Different Route
| Barrier | Route it blocks | Built by |
|---|---|---|
| A safe site | Contamination travelling underground toward the well | Distance and position (Water Table Assessment) |
| A sealed upper section | Surface water running down behind the lining or casing | Surface Seal |
| An apron and drain | Spilled water and rain pooling at the wellhead and soaking in | Sanitary Apron |
| A cover and head | Animals, leaves, children, buckets and hands | A lid; a pump that closes the head (Pump Selection) |
Why Thirty Metres, And Why It Is Not Enough Alone
The rule is a minimum of 30 m between a well and any latrine, animal pen or waste area, with the well uphill. The distance is a proxy for time: bacteria die off and are filtered out as water moves through soil, so more distance gives more time. In ordinary soil 30 m is a common rule of thumb (the figure used in humanitarian water guidance, recalled rather than measured here). It is not a measured safe distance. In coarse sand and gravel contamination travels farther with less filtering; the corpus’s Well Development guide raises the distance to 50 m in sandy or gravelly ground (Well Development). In fissured rock or limestone the distance rule fails completely, because water can run along open cracks for long distances with no filtering at all; there you assume the well is vulnerable and purify the water. Treat the rule as the first barrier, never the only one.
What You Need
- A site chosen by the rules — uphill of every source of contamination
- A sealed upper section — clay, cement or lime mortar
- An apron of concrete or sound masonry — 3 m across, 10 cm thick
- A drain — carrying spilled water away
- A cover — heavy enough that wind, animals and children cannot move it
- A bucket and rope kept off the ground, or a pump that closes the head
Method: Build The Barriers In Order
Step 1: Choose the site before digging. A well cannot be moved afterwards.
Step 2: Seal the top 3 m of the lining, or the top of the hole outside the casing, with clay, grout or cement mortar, and plaster the inside watertight (Surface Seal).
Step 3: Pour the apron. Cast a solid concrete apron 3 m across and 10 cm thick around the wellhead, sloping away from it, and cut a drain from its edge (Sanitary Apron).
Step 4: Raise the lining above ground and cover it. The wellhead stands above the apron and carries a lid.
Step 5: Keep it clean. No livestock near it, no washing at it, no bucket on the ground.
Step 6: Test and disinfect. After construction, and after any repair, disinfect and test the water (Community Water Testing).
Common Mistakes
- No seal. Every storm washes dirt and bacteria in.
- A well too close to a latrine or pen. Fix the siting before building, not after.
- A cracked apron. Water soaks in through the crack.
- A dipped bucket. It brings dirt and hands into the water.
- Trusting distance in limestone. Purify the water.
Safety
A contaminated well makes a whole settlement ill
Cholera, typhoid and dysentery spread through shared water. If the water turns cloudy after rain, smells or tastes wrong, or people fall ill, stop using the well, disinfect it, and find the route in before using it again. Until it is cleared, boil or treat all water from it (Water Purification).
What’s Next
- Learn next: Surface Seal — the barrier against surface water in the hole
- Combine with: Sanitary Apron — the barrier against spills at the wellhead