Size the pump to the WELL, not the demand
The single biggest borehole mistake is buying a pump for how much water you want rather than how much the borehole can give. Every borehole has a sustainable yield — the flow it can deliver continuously without the water level drawing down to the pump. Exceed it and the pump sucks the level down to its intake, loses the water that cools its motor, and burns out. This is the commonest way a borehole pump dies young.
Step 1: Test-pumping (do this first)
A step-drawdown test pumps the borehole at increasing flow rates and measures how far the water level falls at each step. From it you learn:
- the resting water level (before pumping),
- the pumping water level (how far it draws down under load),
- the sustainable yield (the flow the borehole can give continuously).
The Water Resources Authority (WRA) requires test-pumping for good reason — it is the data the whole pump selection rests on.
Step 2: Calculate total dynamic head (TDH)
A pump does not lift water from the borehole's drilled depth — it lifts from the pumping water level, and must also overcome pipe friction and any pressure needed at the surface. Add them up:
TDH = static lift to pumping level + drawdown + friction loss + surface pressure head
Size the rising main generously: undersized pipe adds friction head, so the pump works harder and burns more power forever. Calculate TDH at the worst (deepest) pumping level the borehole reaches in a dry season, not the easy resting level.
Step 3: Match the duty point
Every pump has a curve (more flow = less head). Where it crosses your system's demand is the duty point — the flow and head you will actually get. Choose a pump whose duty point sits near its best-efficiency point, so you get both the flow you need and the lowest energy per cubic metre. A pump with "plenty of head" that operates far from its best point wastes power and wears out.
Step 4: Protect the motor
Two protections keep a borehole pump alive: dry-run (low-water) protection that stops the pump before the level reaches the intake, and adequate cooling flow past the submersible motor (a flow sleeve where the borehole is wide or the pump sits below the inflow). Where demand exceeds yield, the answer is a smaller pump running longer into storage tanks — not a bigger pump fighting the well.
The running-cost number: specific energy
The honest running-cost metric is specific energy — kWh to lift one cubic metre to the surface. It rises with head and falls with pump efficiency. On deep, high-head boreholes this number — and the monthly bill it implies — is exactly what a well-matched pump (and often a solar array) transforms.
The bottom line
Test first, size to the yield, calculate the real head, match the duty point, and protect against dry running. Do that and a borehole pump lasts; skip it and you will be replacing burnt-out motors.
Send us your borehole's test data (yield, water levels, depth) and daily demand and we will select the right pump and depth — and a solar option if it suits. Call +254 768 860 665 or +254 782 914 717.