Source Development

Part of Water Systems

How to find, assess, and develop reliable water sources — springs, wells, streams, and rainwater — for a community water system.

Why This Matters

No pump, filter, or distribution network matters if you have not found a reliable source. Source development is the first step in any water system project, and mistakes made here propagate through everything that follows. A source that appears adequate in a wet year may fail in the third year of drought. A spring that produces clean water most of the year may be contaminated after heavy rain when surface runoff infiltrates the aquifer.

The goal of source development is threefold: find where water is available, understand its quantity and reliability through the seasons, and develop it (protect it, improve its yield if necessary, and connect it to the distribution system) without degrading its quality.

This requires combining observation — reading the landscape for signs of groundwater — with measurement, verification over multiple seasons, and construction skill to protect what you find.

Reading the Landscape for Water

Topographic indicators:

Springs and seeps: Water emerges where the water table intersects the land surface. Look for:

• Breaks in slope on hillsides, especially where permeable rock (sandstone, limestone) meets impermeable rock (clay, granite)
• Persistent green vegetation (willows, alders, reeds) in otherwise dry hillsides — the roots reach the water table
• Permanently damp soil in otherwise dry terrain
• In limestone country: look for caves and sinkholes above the area — they indicate the aquifer structure
• Natural depressions at the base of slopes where runoff concentrates and infiltrates

Valley floor water: Streams are the most visible water source, but their quality is highly variable. Groundwater (from wells or springs) is preferable for drinking because the soil acts as a filter.

Elevated springs: A spring emerging from a hillside above settlement elevation is the ideal source for gravity-fed supply. Note the elevation of any spring relative to the community to determine if gravity supply is feasible.

Geological indicators:

• Sandstone and limestone formations typically yield the best springs — good porosity, good filtration
• Granite and other igneous rocks yield springs mainly from fractures — less reliable
• Clay formations retain water on their surface but yield poor spring flow
• Old maps or local knowledge about historic wells often indicate the best aquifer zones

Seasonal observation:

Never commit to a source after only wet-season inspection. Visit the same springs and streams in the dry season — ideally the end of the driest month. A spring that appears substantial in April may be a trickle or dry in September.

Measuring Source Yield

For springs and small seeps: Build a temporary collection chamber (a stone or clay-lined pit) below the discharge point. Allow it to fill. Measure the time to fill a known volume:

Yield (L/min) = Known volume (L) / Fill time (min)

Repeat at different times of day (yield varies with recent rainfall and ground disturbance). Measure weekly for a month to establish variability. Seasonal measurement over a full year before committing to major infrastructure investment.

For streams: Use the weir method: build a temporary v-notch or rectangular notch in a straight section. Measure head (water depth over the notch) with a ruler. Calculate flow:

• V-notch (90°): Q = 1.38 × H^2.5 (m³/s, H in meters)
• Rectangular weir: Q = 1.83 × L × H^1.5 (m³/s, L = notch width)

For potential well sites: Dig a 0.5 m × 0.5 m test pit to 2 m depth. If water seeps in, time how fast it fills: Recovery rate = Volume collected / Time

This gives a preliminary indication of aquifer yield, though it underestimates the true yield of a properly constructed large-diameter well.

Rainwater Harvesting

Where springs and wells are inadequate, rooftop rainwater collection supplements supply.

Catchment calculation: Volume collected = Rainfall (mm) × Roof area (m²) × Collection efficiency (0.7–0.9) × 1 L/mm/m²

Example: 80 m² roof, 600 mm annual rainfall, 80% efficiency: Annual collection = 600 × 80 × 0.8 = 38,400 liters = 38.4 m³/year

For 4 people at 30 L/day: annual need = 4 × 30 × 365 = 43,800 L. This roof barely meets needs in a wet year. Supplement with a well.

Storage sizing for seasonal rainfall: If 80% of rain falls in 4 months, the tank must store enough to last through 8 dry months: Storage needed = 4 × 30 × 8 × 30 = 28,800 liters ≈ 29 m³. This is a substantial cistern — approximately 3 m × 3 m × 3.3 m deep.

Roof surface materials:

• Fired clay tiles or metal sheet: excellent (minimal contamination)
• Thatch: poor — leaches organic material, bird droppings accumulate
• Untreated wood shakes: acceptable with first-flush diverter
• Painted surfaces: check paint type — lead-based paint is toxic

First-flush diverter: The first 1–2 mm of rainfall per event washes accumulated bird droppings, dust, and pollens from the roof. A simple chamber that fills first and diverts this contaminated first flush to waste dramatically improves water quality. Volume = 2 mm × roof area (liters). A 50 L container on the downpipe for an 80 m² roof (2 mm × 80 m² = 160 L — use a 200 L barrel).

Protecting a Source

A source once found must be protected from contamination. Protection is as important as development.

Spring protection zone:

• Fence an area of at least 30 m radius around the spring head, excluding all animals
• No latrines, graveyards, or waste disposal within 50 m uphill
• No agricultural chemical use within 50 m uphill
• No road drainage directed toward the spring

Stream intake protection:

• Build the intake at least 200 m upstream of any settlement, washing, or animal watering point
• Install a screen to exclude debris and animals
• Protect the streambank above the intake from erosion and trampling

Groundwater protection:

• Seal the annular space around the well casing to 3 m depth with puddled clay or concrete grout — this prevents surface runoff from entering the well alongside the casing
• Build an apron slab around the well head (see well development article)
• Site latrines downhill and at least 30 m from wells (50 m in sandy soils where travel distances are greater)

Source Selection Decision Matrix

When multiple potential sources exist, compare them:

Criterion	Spring	Well	Stream	Rainwater
Reliability	High (if developed)	High	Variable	Seasonal
Water quality	Good	Good	Variable	Good (with first-flush)
Yield control	Seasonal	Pumping-dependent	High but variable	Rainfall-dependent
Treatment needed	Minimal	Minimal	Usually required	Minimal
Infrastructure cost	Low	Medium	Medium	High (storage)
Maintenance	Low	Low-medium	High	Low-medium

A spring above the community with adequate yield is almost always the best primary source. A dug well supplements it. Rainwater harvesting provides backup. Stream intakes are a last resort requiring treatment.

Never develop a single source exclusively unless it has never failed within living memory. The resilient system has multiple sources from different parts of the hydrological cycle, so no single drought or contamination event cuts off the community entirely.