Borehole Storage Tanks: Sizing and Placement

A borehole without a storage tank is a bit like a tap with no geyser behind it — functional in theory, but poorly matched to the way real households actually use water. The pump runs, water moves, but every time someone opens a tap the system reacts to that single draw rather than drawing from a buffer. Adding a correctly sized storage tank changes the whole picture. It protects your pump, smooths out peak demand, and gives you a working reserve when load-shedding or a pump fault cuts supply.

This guide covers how to size a borehole storage tank for a typical Johannesburg home, where to put it, and what the installation usually involves.

Why a storage tank matters for a borehole system

A submersible borehole pump is not designed to switch on and off dozens of times an hour. Every start draws a surge of current and puts mechanical stress on the motor. Without a storage tank, the pump cycles on whenever demand appears — a running tap, a toilet refilling, a washing machine filling. A storage tank breaks that link. The pump fills the tank at its own pace, and your household draws from the tank. The pump runs fewer, longer cycles, which extends its working life considerably.

There is a secondary benefit that matters particularly in Johannesburg: municipal supply interruptions. Johannesburg’s reservoir system holds roughly 27 hours of citywide storage buffer, which sounds reassuring until a local main bursts or load-shedding disrupts pumping stations. A borehole with its own storage tank means your household keeps running independently of both the grid and the municipal network during those windows.

How to size a borehole storage tank

Two figures drive the sizing calculation: your household’s daily demand, and your borehole’s recovery rate (how fast water seeps back into the borehole after pumping).

For daily demand, South Africans use on average about 237 litres per person per day, which is a reasonable planning figure. Multiply that by the number of people in your home. A household of four comes to roughly 950 litres a day under average use; in practice, conscious water users will be lower, and gardens or pools push it higher.

For borehole recovery, your driller’s yield report should state a sustainable yield in litres per hour. If your borehole recovers slowly — common in parts of Johannesburg underlain by hard Witwatersrand quartzites — you need a larger tank to bridge the gap between pump output and demand peaks.

As a rough guide:

Household size	Suggested minimum tank capacity
2 people	1,500–2,500 litres
3–4 people	2,500–5,000 litres
5–6 people	5,000–10,000 litres
Large property / irrigation	10,000 litres+

These are starting points only — confirm the right size with installers who have seen your borehole yield report and your property layout. You can read more about the general tank-sizing logic in our guide on how big a water tank you need, which covers the same principles for any backup water system.

Above-ground or underground tank?

Borehole storage tanks come in two main configurations, and the choice affects both cost and water pressure.

Above-ground tanks (typically polyethylene, on a raised stand or a masonry base) use gravity to create pressure. The higher the base, the more pressure you get — roughly 10 kPa per metre of height. At 2 metres, that is 20 kPa, which is enough for taps and showers but may fall short for some geysers or pressure-sensitive appliances. Most installations pair above-ground tanks with a pressure booster pump to lift pressure to a comfortable level.

Underground or in-ground tanks (fibreglass or polyethylene) keep the tank out of sight and maintain a cooler, more stable temperature that limits algae growth. Water stored underground, however, has no gravity pressure and always requires a booster pump to distribute it through the house.

For most suburban Johannesburg properties, an above-ground tank on a raised base paired with a small booster pump is the most common and cost-effective setup. Our full overview of borehole drilling covers how the pump, tank, and reticulation system connect as a complete package.

Where to place the tank on your property

Placement involves practicalities that are easy to overlook until after installation.

Distance from the borehole: Keep the run of rising main (the pipe from the pump to the tank) as short as practical. Longer runs mean more pipe, more fittings, and slightly more friction loss. Where the borehole is at the back of the property and the tank needs to be near the house, this is usually manageable, but it adds to cost.

Sun exposure: Sunlight accelerates algae growth inside a tank. Situate the tank in shade where possible, or choose an opaque tank rated for UV resistance. Dark-coloured polyethylene tanks are common for this reason.

Access for maintenance: Leave enough clearance around the tank for an installer to inspect the inlet, outlet, overflow, and float valve without difficulty. Squeezing a large tank into a narrow side passage looks tidy but creates headaches later.

Structural support: A 5,000-litre tank full of water weighs roughly 5,000 kg. The base — whether a slab, a brick stand, or a steel frame — must be engineered to carry that load without settling or cracking. This is not an area to cut corners.

Municipal by-law compliance: Johannesburg’s by-laws require that borehole water used for any purpose that could contact human skin or be consumed must meet SANS 241 (2024 edition) drinking-water quality standards. Your installation should include appropriate filtration and, where needed, disinfection before the tank. Cross-connection with the municipal supply line is prohibited without an approved backflow preventer.

Sizing a tank correctly starts with knowing your borehole's actual yield — and that means getting quotes from installers who will assess your site properly. Compare 3 free quotes — vetted installers, no obligation.

What a complete system typically costs

The tank itself is only one part of the installed cost. For context, typical complete borehole systems in Johannesburg run R40,000–R150,000, with most falling between R60,000 and R100,000. Borehole pumps typically cost R15,000–R35,000 installed. A backup tank-and-pump system without a borehole typically costs R20,000–R40,000, with whole-house examples around R55,000.

Where a borehole already exists and you are adding or upgrading the storage tank and reticulation, costs will depend on tank size, stand construction, pipework runs, booster pump specification, and any filtration required. Get itemised quotes rather than lump-sum figures so you can see exactly what each component is contributing to the total.

Maintenance to keep in mind

A storage tank is not fit-and-forget. A few routine tasks keep the system reliable:

• Annual tank inspection and clean: Sediment accumulates at the base. An annual inspection, and a clean every few years, prevents build-up from affecting water quality.
• Float valve check: The float valve controls when the pump fills the tank. A stuck or worn valve can cause the pump to run continuously or the tank to overflow.
• Water quality testing: The Department of Water and Sanitation recommends periodic testing of private water sources. Even if the borehole tested clean at commissioning, conditions in an aquifer can change.
• First-flush inspection after extended non-use: If the system has been idle for weeks, run a flush cycle and retest before using the water for drinking or cooking.

If you are still deciding whether a full borehole system makes sense for your property, talking to a few installers is the quickest way to get realistic numbers. Get your 3 free borehole quotes — no commitment, just clarity.

Putting it all together

A well-sized, well-placed borehole storage tank turns an intermittent pumping system into a reliable household water supply. The pump works less hard, pressure is consistent, and you have a genuine buffer against the interruptions — load-shedding, municipal outages, pump servicing — that are a real part of life in Johannesburg. The upfront thinking on sizing and placement pays for itself in pump longevity and peace of mind.

Water quality compliance and structural soundness are not negotiable: use qualified installers, get your water tested, and make sure your base can carry the load. Everything else is a matter of matching the numbers to your household.