To find groundwater before you dig, combine four clues: low ground such as valley floors and dry streambeds, plants that stay green through the dry season, wells that neighbours already use, and 10-15 cm test holes that show water at a measured depth. Near a river or stream the water table is usually 3-10 m below the surface, and the level that matters is the dry-season low, so dig at least three test holes in different places before you commit to a well site.
Part of Deep Wells
The water table is the surface below which the ground is saturated with water. Assessing it means estimating how deep it lies, how far it falls in the dry season, and which way the groundwater is moving, before any large digging is started.
The Water Table Is Shallowest Where The Land Is Lowest
Rain that soaks into the ground sinks until it reaches soil or rock that is already full of water. The top of that saturated zone is the water table. It is not flat: it follows the land, a little smoothed out, so it lies closest to the surface in valley bottoms, beside rivers and at the foot of slopes, and furthest down under hilltops.
That is why the first rule of siting is to look low. Near a river or stream the water table is usually within 3-10 m of the surface. On a hilltop the same ground may hold water only far below any depth you can dig by hand.
Four Clues Narrow The Search
| Clue | What it tells you | How far to trust it |
|---|---|---|
| Landform | Valley floors, dry streambeds and slope bases have shallower water | Good for choosing where to start looking |
| Plants | Lush green growth in the dry season suggests shallow water | Strong, but confirm with a hole (Indicator Plants) |
| People | Anyone who has lived here knows existing wells, dry spots and seasonal levels | Worth more than any technique; ask first |
| Test holes | The actual depth to water at that spot | The only clue that gives a number (Test Holes) |
Landform and plants say where to dig the test holes. The holes say whether the site is worth a well. For reading slopes and drainage on the ground, see Terrain Reading, and for the first-days version of this search see Ground Sources.
Measure In The Dry Season, Or Allow For It
The water table falls through the dry months and rises after rain. A hole that shows water in the wet season may be dry at the end of summer, and a well dug to the wet-season level will fail exactly when it is needed. If you can only test in the wet season, ask local people how deep their wells run dry, and plan to dig well below the level you measure.
What You Need
- A narrow hole-maker — a hand auger or a digging bar and shovel, to make 10-15 cm test holes
- A weighted line — a stone on a knotted cord, to measure the depth to water
- Notebook and pencil — depth to water, the layers you pass through, and the date for every hole
- A person who knows the area — ask where wells are, how deep they are, and where they run dry
Method: Locate, Test, Compare
Step 1: Ask first. Find out where existing wells and springs are, how deep the water stands, and where the ground stays wet in summer. Mark them on a sketch.
Step 2: Walk the low ground. Look in valley floors, dry streambeds and the bases of slopes for green growth in the dry season. Mark each candidate.
Step 3: Dig test holes. Open at least three test holes at different candidate spots. Each should be 10-15 cm across. Write down the depth at which water first appears and the depth at which it settles.
Step 4: Compare. Prefer the spot with the shallowest settled water, the most promising soil layers, and a position uphill of any latrine or animal pen. A hole that stays dry where the others find water tells you the ground there is poor.
Step 5: Check the site rules. A well site needs at least 30 m between the well and any latrine, animal pen or waste area, and the well must be uphill of them. Groundwater moves downhill, so a source placed uphill of the well sends its drainage towards it.
Why 30 m and why distance alone is not enough
The 30 m figure is a common rule of thumb for how far bacteria are expected to travel and die off in ordinary soil; it is not a measured safe distance. In sandy or gravelly ground water travels farther with little filtering, and in fissured rock or limestone it can carry contamination a long way, fast, along open cracks. In those rocks a distance rule fails completely, and the well must be treated as vulnerable and the water purified (Spring Location covers the same limestone warning).
Common Mistakes
- Testing once. A single hole can land in a pocket of clay or a dry sand lens. Three holes show whether the result is typical.
- Judging from the wet season. The level you need to know is the dry-season low.
- Treating green plants as proof. Green ground can come from a leak, a pond or surface runoff. Confirm with a hole.
- Leaving test holes open. An open hole is a direct path from the surface to the aquifer and a trap for children and animals. Fill each one with clay and soil when you are done.
Safety
Do not climb into a pit to examine it
Test holes are narrow so that nobody needs to go in. If you dig a wider trial pit, do not stand in one deeper than 1.2 m unless the walls are sloped back or shored, keep the dug soil at least 0.6 m from the edge, and never work alone. The wall of even a shallow pit can collapse faster than anyone can climb out.
What’s Next
- Learn next: Test Holes — how to make the holes and read what they show
- Combine with: Indicator Plants — choosing where to put the first hole