Borehole Pump Services

A pump does not lift water from the depth of the borehole — it lifts it from the pumping water level, which sits below the resting level once the pump is running and the well draws down. The pump must then overcome four things added together as total dynamic head (TDH): the static lift to the pumping level, the additional drawdown, the friction loss in the rising main and pipework, and the pressure head needed at the surface (to fill a tank on a tower, or to hold pressure in a network). Size for the resting level alone and the pump runs short of the tank every dry season when the level drops.

Friction loss is the silent thief here: undersized rising main to save a little on pipe costs a great deal in head, so the pump works harder and burns more power forever. We calculate TDH at the worst pumping level the borehole reaches, size the rising main to keep friction sensible, and choose the pump to that duty — not to the borehole's drilled depth, which is a different and irrelevant number.

Every pump has a characteristic curve — as you ask it for more flow, the head it can deliver falls. Your system has its own curve too: the more water you push, the more friction head it demands. Where the two curves cross is the duty point, the flow and head the pump will actually deliver in this borehole. A pump is most efficient only in a band around its best-efficiency point (BEP); run it far to the left (throttled, low flow) or right (over-pumping) and efficiency collapses and the pump suffers.

This is why a pump that "has plenty of head" can still be the wrong pump — if its duty point lands far from its BEP, it wastes energy and wears out. We select so the borehole's real duty point sits near the BEP, which is how you get both the flow you need and the lowest energy per cubic metre. Matching the pump to the curve, not the catalogue maximum, is the whole craft.

The borehole has a limit — its sustainable yield, the flow it can give continuously without the level drawing down to the pump. A proper test-pumping (step-drawdown) exercise measures how far the level falls at increasing flows and reveals that ceiling; the WRA requires it for good reason. A pump sized above the well's yield will draw the level down to its intake, suck air, lose its cooling water and burn out — the single most common way a borehole pump dies young.

So the pump is sized to the well, not just the demand. Where demand exceeds yield, the answer is a smaller pump running longer into storage tanks, plus low-water (dry-run) protection that stops the pump before the level reaches the intake. We set the pump at the correct depth above the screen, fit level protection, and design tank storage to bridge peak demand — so the borehole is harvested at a rate it can sustain for decades.

A submersible motor is cooled by the very water flowing past it, and that flow must reach a minimum velocity or the motor overheats even while pumping. In a wide borehole, or where the pump sits below the inflow, a flow sleeve (cooling shroud) forces the water past the motor to keep it cool. Ignore this and the motor cooks in a well that is, paradoxically, full of water.

Cavitation is the other hidden killer: if the pressure at the pump intake falls below the water's vapour pressure, bubbles form and then collapse violently against the impeller, pitting the metal and destroying efficiency. Adequate submergence (enough water above the intake) and a sensible intake design keep the available suction head above what the pump requires (NPSH), which is what stops cavitation. These are not optional refinements; they are the difference between a pump that lasts ten years and one that fails in two.

The honest running-cost metric for a borehole is specific energy — the kWh needed to lift one cubic metre of water to the surface. It rises with head and falls with pump efficiency, and it is the number that should drive both pump selection and the energy source. A deep, high-head borehole on grid or diesel power can have a surprisingly large monthly bill that a well-matched pump and a solar array transform.

Solar borehole pumping fits the resource beautifully: the sun is strongest when tanks are being drawn down in the heat of the day, and storing water in a tank is far cheaper than storing energy in batteries. A solar-direct pump with a variable-speed drive ramps with the available sunlight, filling storage through the day with no fuel and almost no running cost. For farms, schools and remote sites off the grid, it is often the lowest lifetime-cost water there is.