Choosing the Right Borehole Pump Size

Buying a borehole pump without proper sizing data is one of the most common — and most expensive — mistakes Johannesburg homeowners make. You end up with either an underpowered pump that can’t keep up with demand, or an oversized one that outpumps the borehole’s recovery rate and runs dry. Neither outcome is cheap to fix. This guide explains the key measurements involved and the questions you should put to any installer before signing off on a spec.

Why sizing matters more than brand

A pump is essentially a machine that adds pressure to water to move it from one point to another. How hard it has to work — and therefore how big it needs to be — depends entirely on the specific conditions of your installation. Two boreholes drilled fifty metres apart in Johannesburg can have completely different depth and yield profiles, so there is no universal “right” pump. Getting the spec right means the pump runs in the middle of its efficiency curve: not labouring at maximum capacity, not spinning at a fraction of its rated load. Both extremes shorten its life significantly.

The three numbers you need before anything else

1. Static water level (SWL) This is how far below the surface the water naturally sits when the borehole is at rest. It is measured in metres and comes from your drilling report. In parts of Johannesburg the water table can sit anywhere from a few metres down to well over a hundred metres, depending on geology.

2. Dynamic water level (DWL) and yield When you start pumping, the water level drops — this lower point is the dynamic water level. Your drilling report should also state the tested yield in kilolitres or litres per hour. This is the single most important constraint: your pump must never be sized to pump faster than the borehole can recover, or it will run dry and burn out the motor.

3. Total Dynamic Head (TDH) This is the total pressure load the pump must overcome. It combines the dynamic water level (the lift from underground), the vertical height from ground level to your storage tank or header tank, any friction losses in the pipework, and any pressure needed at the delivery point. TDH is what a reputable installer uses to select a pump from a manufacturer’s performance curve.

How installers match pump to borehole

Once a driller has those figures, they plot the required flow rate against the TDH on a pump performance curve — a graph supplied by the pump manufacturer. The aim is to find a pump whose duty point (where it will actually operate) sits near the middle of the curve, in the highest-efficiency zone. A pump operating far to the left or right of this zone is inefficient and wears faster.

For most Johannesburg homes a submersible pump is used — it sits in the water column inside the borehole casing rather than above ground. If you want to understand what this type of unit typically costs once properly installed, the detailed breakdown at /blog/submersible-borehole-pump-cost/ is worth reading before you get quotes. As a broad guide, borehole pumps typically cost R15,000–R35,000 installed, though installations with greater depth, longer surface pipe runs or more complex electrical work can fall outside that range — get itemised quotes to confirm.

Common sizing mistakes to watch for

Oversizing for “future-proofing” Installers sometimes recommend a larger pump on the basis that you might add irrigation or an extra bathroom later. This sounds sensible but can be a problem if the borehole yield does not support the higher flow rate. Always check that the proposed pump’s maximum flow rate is below the tested yield.

Ignoring friction losses Long horizontal pipe runs, multiple bends and narrow pipe diameters all add friction resistance, which effectively increases your TDH. A quick calculation on paper is fine; ignoring it and then wondering why water pressure is weak at the tank is not.

Using a single-phase pump on a low-capacity circuit Many Johannesburg homes have ageing DB boards. A pump that draws heavy startup current can trip breakers or cause voltage dips that damage the motor over time. Your electrician and your pump installer need to be in communication.

Not specifying a pump controller or protection relay Dry-run protection, overload cutouts and phase-failure relays are not extras — they are basic protection for a piece of equipment that may cost R20,000 or more. Any quote that omits them should be queried.

If you're ready to get a properly sized borehole system specified for your property, compare 3 free quotes — vetted installers, no obligation.

What your drilling report should contain

If you already have a borehole or are commissioning one, insist on a written drilling report that includes at minimum:

Item	Why you need it
Static water level (metres)	Sets the minimum lift requirement
Dynamic water level at test pump rate	Shows how far the level drops under load
Tested yield (litres per hour or kl/hr)	Hard ceiling for pump flow rate
Borehole depth and casing diameter	Determines which pump body sizes physically fit
Geological log	Useful if problems occur later
Water quality sample results	Needed to confirm compliance with SANS 241

That last point is worth emphasising: South Africa’s drinking-water quality standard is SANS 241 (2024 edition). Borehole water is not automatically safe to drink, and the pump specification has no bearing on water quality — you need a separate test and, if necessary, treatment. The Department of Water and Sanitation (DWS) publishes guidance on groundwater use and quality obligations that is relevant to any homeowner considering borehole water for potable use.

Practical questions to put to any installer

Before you approve a pump spec, ask the installer to walk you through the following:

• What TDH figure have you used, and how was it calculated?
• What is the pump’s rated flow at that TDH, and how does that compare to the tested yield?
• Where does the duty point sit on the manufacturer’s performance curve?
• What protection devices are included in this quote?
• What cable size and length has been used in the costing, and why?
• Is the borehole casing diameter compatible with the pump body diameter?

A competent installer will answer all of these without hesitation. Vague answers or irritation at the questions are useful data.

Unsure whether a quote you've received is well-specified? Get two or three competing quotes to compare specs side by side — vetted installers, no obligation.

Pulling it together: what good sizing looks like

A well-sized pump for a typical Johannesburg home will have a flow rate comfortably below the tested borehole yield, a TDH calculation that accounts for all pipe runs and elevation changes, a duty point in the efficient middle portion of the performance curve, and dry-run and overload protection built in. The full cost of a complete borehole system — pump, casing, pipework, controls and electrical connection — typically runs R40,000–R150,000, with most residential installations falling between R60,000 and R100,000. The pump is a significant but not dominant part of that total.

For a fuller picture of what the overall installation involves, the borehole drilling guide covers the end-to-end process from site assessment through to commissioning. Sizing the pump correctly is one step in that process — but it is the step that determines whether your system runs reliably for a decade or causes headaches within the first year.