Estimate a site’s well potential before digging by reading the land: ground that stays green in drought, low ground between hills, gravel over clay, and any old well you can measure at the end of the dry season. Hand-dug wells are feasible to about 10-15 meters, so a site where water lies deeper than that, or where the dry-season water table is out of reach, needs a different source.
Reading landscape, vegetation and nearby wells to predict the depth and reliability of groundwater at a candidate settlement site.
Water Lies Closest to the Surface in Low Ground, and Falls Every Dry Season
Rain that soaks in fills the spaces in the soil and rock until it meets a layer that stops it. The top of that saturated zone is the water table. It rises after rain and falls through the dry months, so a well dug in the wet season can run dry in the dry season. The carrier names the signs of reachable groundwater: vegetation that stays green in dry periods in specific areas, low-lying ground between hills with shallow water tables, gravel over clay layers that hold water, and the remains of old wells.
What You Need
- A weighted string or rope — to measure depth to water in existing wells.
- A shovel or auger — for a test hole.
- A notebook — dates matter, because the water level changes.
Method: Estimate Before You Dig
Step 1: Read the plants Willow, alder, reeds and rushes growing in an otherwise dry patch point to shallow water. Check whether they are green when everything around them has dried.
Step 2: Read the shape of the land Water table follows the land surface in a muted way. It sits nearest the surface in valley floors and near streams, and deepest under ridges and hilltops. Springs on the valley sides mark places where the table meets the surface.
Step 3: Measure existing wells If any well exists nearby, measure from the rim to the water and record the date. Repeat at the end of the dry season. The difference shows how much the level moves; your own well must be dug deeper than the lowest reading.
Step 4: Dig a test hole Dig a hole in the likely spot; note the depth at which damp soil begins and the depth at which water seeps in. Do not rely on a wet-season hole.
Worked Example
A neighbouring well, measured at the end of a wet season, has water 6 m below the rim. At the end of the dry season the same well has water 8 m below the rim.
- Seasonal fall: 8 m - 6 m = 2 m.
- A well dug beside it should reach the dry-season level plus a working column of water to draw from, say 2 m: 8 + 2 = 10 m below the rim.
- That is inside the carrier’s hand-dug range of 10-15 m, but at its lower edge. A site where the same sums give more than 15 m should look at springs or surface water instead.
Common Mistakes
- Using a wet-season depth as the design depth — dig to the dry-season level plus a margin.
- Digging in the first wet spot — a perched pocket of water can stop short of the real water table and vanish in summer.
- Placing the well near a latrine — see below.
Safety
Wells kill diggers and contaminate the people who drink from them
Latrines: keep every latrine or pit at least 30 m from any well, downslope of it, and with the pit bottom well above the water table (humanitarian guidance such as the Sphere Handbook gives 30 m and 1.5 m; more in sand, gravel or fissured rock). Digging: oxygen can be low and carbon dioxide or methane can collect at the bottom of a well. Never descend into a well that has not been ventilated, never rely on smell, and do not test the air with a flame because methane burns. See Well Digging: Hand-Dug Water Wells for the full procedure.
What’s Next
- Learn next: Well Digging: Hand-Dug Water Wells — digging and shoring the well
- Combine with: Watershed Position & Flood Risk — where the water table meets the flood line