Well Development

Part of Water Systems

How to site, dig, line, and complete a dug well that yields clean, reliable water year-round.

Why This Matters

A properly developed well is among the most valuable infrastructure assets a community can have. Unlike surface water, groundwater is naturally filtered by passage through soil, protected from direct contamination, and available year-round in most aquifer types. A good well sited in the right place with proper protection and lining can supply clean drinking water for generations.

Poorly developed wells are worse than useless. A well dug in the wrong location may yield contaminated water from the beginning. A well without a proper headwork admits surface contamination continuously. A well with no lining collapses and injures workers or users. Understanding the full sequence — site selection, excavation, lining, headwork, and commissioning — is essential for building infrastructure that truly improves health rather than creating a false sense of security.

Siting a Well

Geological assessment: Wells produce water from aquifers — saturated zones of permeable soil or rock. The most productive dug wells are in:

• Alluvial valleys: Sand and gravel deposits beside rivers hold abundant groundwater, typically 3–8 m depth
• Weathered rock: Many rock types weather to a clay-sand mixture near the surface that holds water above the unweathered rock
• Fractured rock: Springs emerging from hillsides indicate fractures that continue to depth

Avoiding contamination: The primary sanitary rule: site wells at least 30 m horizontally from latrines, septic tanks, animal pens, solid waste disposal areas, and any buried waste. In sandy or gravelly soils, increase this to 50 m. Always site the well uphill from contamination sources — groundwater flows in the direction of the water table slope (generally same direction as surface topography).

Test well (trial pit): Before committing to a full well, dig a 0.5 m × 0.5 m test pit by hand to 2 m depth at the intended site. Observations:

• Does water seep in within 30 minutes? At what depth?
• What is the soil profile? Sandy or gravelly zones will yield more than clay.
• Does the water clear up after bailing, or does it remain persistently turbid? Turbid-always water comes from a poor aquifer.
• What color is the water? Yellow/brown may indicate surface contamination. Clear is good.

Water table depth: The seasonal water table fluctuation determines the required well depth. The well must penetrate at least 2–3 m below the lowest seasonal water table (end of dry season). Ask local farmers how deep their wells run dry — this gives the seasonal low.

Excavation

Safety in well digging:

• Toxic gases: Methane, carbon dioxide, and hydrogen sulfide can accumulate in wells. Test before entry: lower a lit candle into the well. If it goes out before reaching the bottom, the air is deficient in oxygen or rich in combustibles — do not enter. Ventilate by swinging a cloth vigorously at the top of the well for 10 minutes, then retest.
• Collapsing walls: Never work in an unsupported well in loose soil. Install temporary planking around the perimeter as you go down.
• Lifting equipment: Use a proper windlass or A-frame pulley for lifting spoil. Never improvise with rope thrown over a branch.
• Working alone: Always have a second person at the surface when the digger is underground.

Excavation diameter:

• Minimum: 0.9 m (very cramped — avoid if possible)
• Comfortable working diameter: 1.2 m
• Final well diameter accounts for lining thickness: inner bore = working diameter + 2 × lining thickness

Excavation sequence:

1. Mark the circle with a compass (string and stake)
2. Dig to 1.0 m and install the first ring of temporary planking (upright boards or split poles around the circumference)
3. Continue down 0.5–1.0 m at a time, installing planking as you go
4. Loosen soil with a pick, fill buckets, signal to surface worker to haul
5. Rotate digger and surface worker every 30–45 minutes (confined space work is tiring and slightly hypoxic)
6. When water seeps in heavily (within 0.3 m of the water table), stop and bail — determine whether the inflow rate allows continued digging or whether you need to work fast and line before further water entry
7. In good aquifer material, dig 2 m below the water table for yield
8. In tight clay aquifer, stop at 1 m below water table

Dealing with boulders: Wet the boulder and light a fire on and around it for 30–60 minutes. Quench suddenly with water — thermal shock fractures most rock types. This method (fire-setting) was used for well and mine excavation for thousands of years.

Lining the Well

Why line? The lining serves two purposes: structural support (prevents collapse) and sanitary protection (seals the upper portion against surface contamination infiltration).

Lining materials (in preference order):

1. Fired brick in hydraulic lime mortar — best combination of strength, sealing, and availability
2. Dressed stone in hydraulic lime mortar — excellent where stone is abundant
3. Dry-stone (no mortar) — allows water entry throughout the lining; acceptable in the lower zone where inflow is desired, not for the upper 3 m
4. Timber cribbing (wood frames) — adequate in dry climates but rots within 5–10 years in permanently wet conditions

Lining construction:

1. Build rings of brick or stone from the bottom up, working inside the excavated cylinder
2. Use a plumb bob continuously — the lining must be vertical
3. For the bottom 2–3 m (in the aquifer), leave open joints (no mortar) or use dry-stack to allow water to enter from the aquifer
4. For 3 m below ground level upward, use solid hydraulic lime mortar with no gaps — this is the sanitary seal zone
5. Render the inside of the upper 3 m with hydraulic lime render, 2 coats, trowelled smooth — prevents surface water seeping through the lining

Sanitary seal (critical): The annular space between the outside of the lining and the excavated earth wall must be grouted in the upper 3 m. Fill with puddled clay, rammed concrete, or poured lean concrete. This prevents surface-derived contamination from channeling down the outside of the lining into the aquifer.

Without this seal, a well that appears clean may be systematically contaminated with every rainfall event.

Well Head Construction

The well head must:

• Prevent contamination from entering the well
• Support safe water lifting
• Drain spillage away from the well

Components:

1. Raised well wall: Extend the lining 0.5–0.75 m above ground level. This prevents surface runoff, animals, and children from entering the well.
2. Apron slab: A 1.2 m × 1.2 m concrete or stone slab around the well head, sloped at 1:20 to drain all spillage away from the well. Slope toward a drainage channel leading at least 5 m from the well.
3. Drainage channel: Stone-lined, discharges to a soakaway pit at least 5 m from the well.
4. Cover: A tight-fitting concrete or timber lid over the well opening. Can be hinged for access. Must prevent insects, small animals, and light (algae grows in sunlit wells) from entering.
5. Windlass or pulley: A wood-framed A-frame or horizontal drum windlass to raise water. The drum accumulates rope so that the bucket is raised steadily without effort proportional to the depth.
6. Dedicated bucket: A single bucket kept at the well (tied to the rope), not shared with other uses. Communal buckets spread contamination. The bucket itself should not touch the ground — hang it on a hook.

Commissioning and Development

After lining and headwork construction:

Initial development: Bail the well vigorously with a large bucket, raising and lowering it at the bottom to disturb the aquifer and draw fine particles out. Continue until the water runs clear. This may take 30–60 minutes of bailing.

Disinfection:

1. Calculate the water volume in the well: V = π × r² × depth of water (r = inner radius)
2. Add chlorine to achieve 50 mg/L (much higher than drinking dose): for 2,000 liters of water in the well, add 2 liters of 5% bleach
3. Stir the well with a pole to mix
4. Leave 24 hours
5. Bail the well completely — haul all water out and discard
6. Allow the well to refill naturally
7. Test for chlorine residual — if still strongly positive, bail again and refill

Yield test: Note the water depth before the test. Bail continuously for 1 hour with the largest bucket available. Measure the new water level (it will have dropped). Stop bailing. Note the time for the level to recover by 0.5 m. Recovery rate = 0.5 m × well cross-section area / recovery time — this is the sustainable yield in m³/hour.

If yield is adequate for community needs: proceed. If insufficient: may need to deepen the well or investigate a different site.

Annual Maintenance

• Inspect the apron slab for cracks — repair immediately (crack = contamination pathway)
• Check the cover for fit — replace if warped or cracked
• Bail and check the water level and clarity
• Inspect the lining for damage
• Verify drainage channel is unblocked
• Disinfect with chlorine dose every 5 years, or after any flooding event