Wild water and wells

Groundwater is not an underground lake. It is water filling the spaces between grains of sand, gravel and fractured rock, and its upper surface — the water table — follows the shape of the land in a flattened way, closest to the surface in valleys and near rivers.

The signs, in rough order of reliability:

• Springs and seeps. Water already reaching the surface. Wet patches, green lines across a dry slope, and moss at the base of a cliff all mark groundwater within reach.
• Water-loving vegetation in dry country. Willows, poplars and cottonwoods, reeds, rushes and sedges, and date palms put their roots into the water table. A line of green trees across dry land is often following a buried stream.
• Valley bottoms and the foot of slopes. The water table is nearest the surface there.
• Dry riverbeds. Water often flows under the sand long after the surface is dry. Dig at the outside of a bend, where the flow scoured deepest, and at the lowest point — water commonly appears 0.5–2 m down.
• Animal tracks converging, and insects and birds circling low at dawn and dusk.

What does not work, however confidently it is taught: water divining with rods or a forked stick. Controlled trials have repeatedly found diviners do no better than chance. Dig where the ground says water is.

Choose by what the ground allows, then by how well each can be protected.

Hand-dug wells kill diggers every year, and almost always in one of four ways. Each has a rule.

Dig in the dry season. The water table is at its lowest. Dig at least 1–2 m below the dry-season water level — a well dug in the wet season, stopped where water first appears, is dry by the end of the next dry season.

Size: about 1.2–1.5 m inside diameter — room for one person to dig, no more. A wider shaft means more spoil and more collapse risk for no gain in yield.

Line it as you go. Concrete rings, brick or stone, advanced down the shaft in stages. Sand and gravel collapse without warning; clay that stands for a day can slump overnight, especially once it gets wet.

1. Bad air — test before every descent. Carbon dioxide is heavier than air and pools at the bottom of shafts. Lower a lit candle or lamp to the working depth. If the flame dims or goes out, nobody goes down. Ventilate — lower a burning bundle and pull it up repeatedly, or fan air down — and test again.
2. Engines never go in or near the shaft. A petrol pump or generator in or beside a well fills the shaft with carbon monoxide. This kills rescuers too: the second and third deaths in a well are usually people who climbed down after the first.
3. Nothing is carried over the opening. A dropped hammer or stone falling 15 m kills. The person below wears a hard hat; the people above keep tools away from the edge, and lower everything in a bucket.
4. Always two people, and a rope that can pull the digger out — tied off, not held.

Nearly all well contamination enters from the top: spilled water carrying mud and dung back down the outside of the lining, surface runoff after rain, animals, and the bucket and rope that were put down on the ground. Seal the top and most of the risk is gone.

1. Seal the lining for the top 3 m. Mortar or grout between the rings and behind them, so surface water cannot run down the outside of the shaft and into the aquifer. Below that depth the lining is perforated or open-jointed in the water-bearing layer, with a gravel pack behind it, so water can enter.
2. A headwall at least 0.5 m high above the ground — keeps runoff, animals and children out.
3. A concrete apron at least 1.5 m wide all round, sloping away from the well.
4. A drainage channel from the apron edge to a soak pit or garden at least 6 m away — never a puddle at the well.
5. A cover. A lid, a hand pump, or a windlass house. An open top is an open wound.
6. One dedicated bucket and rope that never touch the ground, hung on a hook. Better, a hand pump, which removes the bucket from the system altogether.
7. A fence keeping animals at least a few metres off.

And site it: at least 30 m from any latrine, and uphill of it. See the sanitation guide.

The 7-metre rule decides the equipment.

• Water table within about 7 m: a suction hand pump at the surface works. The classic cast-iron pitcher pump and the driven well point are this category. At altitude the limit falls — roughly 1 m less for every 1,000 m of elevation.
• Deeper than 7 m: the pumping element has to be down in the water, pushing up rather than pulling. A rope pump — a loop of rope carrying washers up through a pipe, turned by a wheel — is buildable from salvage and works to about 30–40 m, with output falling as depth rises. Deep-well piston pumps with the cylinder below the water line go further.
• A bucket and windlass works at any depth, and is the most contaminating option. If it is a bucket, it is one bucket, on its own rope, that never touches the ground.

A well yields what the aquifer feeds it, not what the pump can draw. If a pump brings the level down to the intake and the flow falls away, the well is being over-drawn; pumping in shorter sessions with recovery time between them delivers more water over a day.

A spring is groundwater arriving at the surface on its own, and it is usually excellent water for the first metre of its journey — before feet, animals and rain get to it. A spring box captures it at that first metre.

1. Dig back to the eye of the spring — where water actually emerges from rock or gravel — not the wet patch below it.
2. Pack the eye with clean gravel and build a collection box of masonry or concrete over it, with no opening to the surface except a lid.
3. Two pipes out: an outlet to the collection point, and an overflow set lower than the eye so water never backs up and forces a new outlet elsewhere. Screen both ends against insects and animals.
4. A diversion ditch uphill of the box, carrying surface runoff around it.
5. A fence keeping animals out of the ground above and around the spring — at least 10–15 m.
6. Nothing in the catchment above — no latrines, no livestock pens, no graves.

Then draw water from the outlet pipe, never from the box.

Rain is close to distilled water when it falls. The contamination comes from the roof, the gutters and the tank.

Yield:

> litres per year = roof area (m²) × annual rainfall (mm) × 0.8

The 0.8 is the runoff coefficient for a metal or tile roof — some water splashes, evaporates or overshoots the gutter. A 50 m² roof under 800 mm of rain a year gives 32,000 litres — about 88 litres a day averaged over the year, enough to drink and cook for a household if it can be stored through the dry months.

Keeping it clean:

• Divert the first flush. The first rain washes dust, bird droppings and leaves off the roof. Send the first 1–2 litres per square metre of roof to waste — a vertical pipe that fills and seals with a floating ball before water reaches the tank.
• Screen the inlet against leaves and mosquitoes.
• Cover the tank completely and keep it dark. Light grows algae; an open tank breeds Aedes mosquitoes within a week.
• Draw from a tap above the bottom, never by dipping.
• Roofs to avoid: thatch gives brown, bitter water; lead flashing and old lead paint put lead in it; asbestos cement is a hazard to the people cutting it more than to the water. Metal sheet and fired tile are best.

Clear, cold, odourless water can still carry faecal bacteria, arsenic, nitrate or fluoride. None of them can be tasted at dangerous levels.