Installing a Borehole Pump in Kenya: Sizing, Setting Depth and Commissioning It to Last

A submersible pump gives you one honest chance. The day it goes down the hole, every decision you have made about sizing, setting depth, cable and protection is sealed under tens of metres of water and steel casing. Get them right and the pump can run for years, barely noticed. Get them wrong and no amount of careful use afterwards will save it, because the faults are now beyond your reach and the only cure is to pull the whole assembly back to the surface.

This is what makes borehole pump installation in Kenya so unforgiving. A surface pump sits where you can see it, adjust it and change a part in an afternoon. A submersible pump is buried machinery: you commission it once, and you live with that commissioning until the day it comes back up. The good news is that the decisions are all knowable in advance, and almost every one of them is made at the surface with a completion report, a calculator and the right fittings, long before anything is lowered.

This guide walks through the install itself: reading the borehole before you choose a pump, sizing to head and yield rather than to depth, where the pump should hang and how far above the intake, the riser and cable that carry it, the control box that protects it, and the commissioning steps that prove it works. If you are still deciding between pump types, read our comparison of a submersible against a surface pump first, and if the hole itself is not yet drilled, start with borehole against shallow well. Here we assume you have a hole, a report, and a pump to put in it.

Start With the Borehole, Not the Pump

The most important document in the whole job is the one you already have: the driller's completion report. It records the total drilled depth, the position of the screened (slotted) section that lets water in, the static water level where the column rests when nothing is pumping, and the tested yield with the pumping level measured at that rate. Those four facts describe what the ground can give. The pump is chosen to fit them, never the other way round.

The commonest installation error begins right here, before a pump is even bought. A buyer picks a pump because it promises more water, without checking what the aquifer can sustain. Yield is set by the ground, not by the machine. A pump that outpaces the yield simply drags the water level down to its own intake and starves itself within an hour, then trips or overheats. Match the pump to the tested yield first, and treat every other number as secondary.

Sizing is really a two part question: how much water per hour you need (flow), and how much resistance the pump must push against to deliver it (head). We work through the arithmetic in sizing a water pump by total head and flow. In this article we apply that thinking to a borehole, where the head is dominated by how far the water has to be lifted from the pumping level to the surface.

Total Dynamic Head: Size to the Job, Not the Depth

Total dynamic head is the sum of everything the pump works against. It is the vertical lift from the pumping water level up to the wellhead, plus an allowance for drawdown as the level falls under load, plus friction losses in the riser pipe, plus the further rise from the wellhead to the tank inlet, plus any pressure you need at the outlet. It is emphatically not the depth of the hole.

That distinction is where money is lost. A borehole drilled to 120 metres whose water sits at 45 metres does not need a pump rated for 120 metres of head. It needs one rated for the head at the pumping level plus the surface work, which may be little more than half that figure. Size to the depth by reflex and you buy a pump that is grossly oversized on head, runs far off its best efficiency point, wastes power on every run, and hammers the aquifer harder than it can bear.

Pumping level lift Drawdown allowance Riser friction loss Rise to the tank Outlet pressure

Friction loss deserves its own moment because it is invisible until the power bill arrives. A riser that is one size too narrow adds head the pump must fight on every litre, turning into wasted energy hour after hour. Over a long drop, a slightly wider rising main often pays for itself in electricity and in a pump that runs cooler and lasts longer.

Setting Depth: Where the Pump Hangs and the Clearance It Needs

Setting depth is how far down the pump is suspended on the riser, and it obeys three rules that pull in different directions. First, the intake must sit comfortably below the pumping level, with a submergence margin, so it stays under water during the hardest pumping in the driest month. Second, the motor should hang above the screened section rather than down in the sump, so the water drawn in flows up past the motor shell and cools it. Third, the pump must never rest on the bottom of the hole, where it sits in silt, loses its cooling flow and swallows sediment.

That cooling point catches people out. A submersible motor is cooled almost entirely by the water moving up its outer shell toward the intake. Set the pump too low, in a blind pocket beneath the screen, and water enters above the motor with nowhere to flow past it, so the motor bakes in still water even though the hole is full. Where a pump has to sit low, or in a wide diameter casing where the water moves slowly, a flow sleeve (a shroud around the motor) forces the incoming water past the motor and restores the cooling.

How much margin is enough? The driller's pumping level tells you where the water settles at the tested rate. Add to that a margin for dry season decline, when the whole water table can drop, and set the intake below the deeper of those figures. It is far cheaper to set a pump slightly deeper at installation than to pull it in a drought because the level fell past the intake and the dry-run protection now stops it every afternoon.

The Riser: The Pipe That Carries the Weight

The riser, or rising main, carries three loads at once: the water, the pump, and its own weight. Two families are common in Kenya. Galvanised steel riser, joined by threaded couplings, is rigid and strong and suits deep, heavy sets, but it is heavy to handle and, over years, scales and corrodes on the inside. HDPE riser comes on a coil, is light and free of corrosion and goes in quickly, but it depends on correct compression or fusion fittings and it must be carried by a proper safety rope, because the pipe is not designed to be the only thing holding the pump.

A non-return valve keeps the rising main full between runs. Most submersible pumps have one built into the discharge; on a long riser a second line check valve near the surface stops the whole column draining back and slamming the pump on every stop, a shock known as water hammer that loosens joints and fatigues the pump over time. The balance to strike is not to stack too many check valves, because air trapped between two closed valves creates its own problems. One at the pump and, on tall lifts, one more up the line is the usual pattern.

Three small fittings separate a professional install from an amateur one. A torque arrestor sits between the pump and the casing to absorb the twist the motor delivers on every start, which would otherwise chafe the pump and cable against the casing wall. The cable is clipped or taped to the riser at intervals so it cannot swing and rub through. And a stainless safety rope is tied off at the wellhead, so that if a coupling ever lets go, the pump hangs on the rope instead of falling to the bottom of the hole, where it is often unrecoverable.

Drop Cable and the Splice: The Cheapest Part That Fails the Most

Submersible drop cable is built for permanent immersion, and two decisions about it decide whether your motor survives. The first is size. Over a long drop, an undersized conductor loses voltage, so the motor draws more current for the same work and runs hotter, quietly shortening its life. Cable size is a calculation from the motor current, the length of the run and the permitted voltage drop, not a matter of using whatever offcut is on the van. Getting it right at installation costs a little more copper and saves a motor.

The second is the splice. Every install joins the motor lead to the drop cable, and that joint spends its entire life underwater, under pressure. Made properly with a heat-shrink or resin-filled kit, it seals each conductor and then the whole bundle. Made with insulation tape, it leaks: water tracks along the copper, the insulation resistance to earth collapses, the earth-leakage protection begins tripping, and the motor burns. A taped splice is the single commonest reason a perfectly good pump gets pulled. We go deeper into why joints and cables fail in borehole pump maintenance, but the cure is to insist on a proper kit at installation.

The Control Box and Protection: Buying the Insurance

The control box at the surface is where real protection lives. On a single-phase pump it holds the correct run and start capacitors; on three-phase it holds a starter, either direct-on-line or, for larger motors, a soft starter that eases the start current and reduces the water hammer of a hard stop. Around the starter belong the devices that stop the pump before something expensive happens: an overload set to the motor plate current, dry-run protection, undervoltage and overvoltage protection for a supply that sags or spikes, and, on three-phase, phase-failure and imbalance protection, because losing one phase cooks a motor quickly and silently.

Two more things matter on rural Kenyan supplies. Surge protection with a sound earth is not optional on exposed feeders, where lightning is a recurring cause of pump loss. And the box itself needs a good home: dry, shaded, ventilated, lockable, and sealed against ants and rodents that otherwise nest in the contactor. Never respond to a device that keeps tripping by winding it up. A trip is information about the supply, the water level or the pump, and overriding it converts a warning into a burnt motor.

Priming and Commissioning: Proving the Install

A submersible pump has no suction lift to prime the way a surface pump does, because it already sits in water. Priming here means filling and bleeding the rising main and the delivery pipework, and above all confirming the pump is fully submerged before it is ever energised. Bumping a pump that might be hanging above the water, even for a second, is one of the fastest ways to damage a new motor.

Commissioning is a short, disciplined sequence, and skipping it is where good installs go wrong. On three-phase, confirm the rotation, because a pump running backwards still delivers some water at lower pressure and fools the eye; swap two phases, compare the output, and keep the connection that gives more. Measure the running current on each phase against the motor plate. Throttle the delivery valve to bring the pump to its intended duty point, so it is not running off the end of its curve and overloading. Set and test the dry-run cut-out by simulating a low level. Then record the baseline.

The baseline is the paperwork that pays you back for years. Record the running current on each phase, the flow (time how long the pump takes to fill a container of known size), the delivery pressure, the setting depth, the cable size and the control box settings. Insist on the completion report, the pump and motor plates and the splice type in the same file. A borehole with this record is diagnosed in an hour when something changes; one without it is diagnosed by guesswork and replaced parts.

The Mistakes That Burn Out a Pump Early

Almost every early failure traces back to an install decision, and the same handful recur. Oversizing on flow so the pump outpaces the yield and starves itself. Sizing to the drilled depth rather than the total dynamic head. Setting the pump on the bottom, or below the screen without a flow sleeve, so the motor loses its cooling. A taped splice instead of a proper kit. Undersized drop cable that runs the motor hot. No dry-run protection, or a tank without a level switch, so the pump keeps running when the water is gone. No non-return valve, or too many. No torque arrestor and no safety rope. And, on three-phase, a pump left running backwards because nobody checked the rotation.

None of these are exotic. They are the ordinary shortcuts of a rushed install, and any one of them can turn a pump that should last many seasons into a warranty argument within months. The defence is a contractor who works to the completion report, uses the right fittings, and hands you a commissioning log at the end. Talk to us about pumps, risers, cable, control gear and protection in our water equipment range, and see indicative figures on the price list before you commit.

Frequently Asked Questions