Borehole Testing: Yield Tests vs Water Quality Tests and Which You Need

If you ask a contractor about ‘borehole testing’ and they quote you without asking which kind you mean, that is a small warning sign. The term covers two entirely different exercises with different purposes, different costs and different specialists. Getting clarity on both before you commit money is the sensible starting point.

What yield testing actually measures

A yield test — usually called a pump test or aquifer test — measures how much water a borehole can deliver sustainably over time. The basic question is: if you run a pump, how quickly does the water level drop, and does it recover fast enough to keep up with your household demand?

The simplest version is a stepped constant-rate test: water is pumped at increasing rates while the drop in the water level (drawdown) is logged at set intervals. A basic test might run for a few hours; more rigorous tests for irrigation or commercial use can run for 24–72 hours and include a recovery phase after pumping stops.

What you get at the end is a sustainable yield figure — typically expressed in litres per hour or kilolitres per day. This number directly determines what size pump is appropriate and whether the borehole can realistically supply your needs. Installing an oversized pump without yield data is a common and costly mistake: you can pump a borehole dry and damage the aquifer formation.

For a thorough explanation of what the process involves and what the results mean in practice, the borehole yield testing explained guide on this site walks through the methodology in plain language. Yield testing is normally carried out by the drilling contractor or a specialist geohydrologist, and it is standard practice before a pump is permanently installed as part of any complete borehole drilling project.

What water quality testing actually measures

A water quality test is a laboratory exercise, completely separate from pump testing. It analyses a water sample for physical, chemical and microbiological parameters to determine whether the water is safe for its intended use — drinking, cooking, irrigation, livestock or industrial processes.

The relevant South African standard is SANS 241 (2024 edition), which sets limits for drinking-water quality. An accredited lab measures things like pH, turbidity, nitrates, fluoride, heavy metals, coliform bacteria and E. coli. You receive a report comparing your results against those limits.

Crucially, borehole water quality varies enormously depending on the geology, depth and local land use. A borehole in a residential suburb may return clean results; one near an old agricultural holding or informal settlement may show nitrate contamination or faecal bacteria. You cannot tell from appearance or taste alone.

For a breakdown of what labs charge and what different test panels include, see how much borehole water testing costs. And because quality can change over time — seasonal rainfall, nearby construction and ageing casing all affect results — how often you should test borehole water explains a sensible ongoing schedule.

Who does each test

These two types of testing involve different people entirely.

Test type	Who carries it out	When it happens
Yield / pump test	Drilling contractor or geohydrologist	Before permanent pump installation
Water quality test	Accredited laboratory (SANAS-accredited)	After drilling; then periodically

Drillers are not laboratories. A drilling company that offers to hand you a water quality result without sending a sample to an accredited lab should prompt a follow-up question about their accreditation. Conversely, a laboratory cannot assess whether your aquifer has enough yield to run a household — that requires on-site pump equipment and hydrogeological interpretation.

When you need each type

Yield test: always, before pump installation. Whether you are drilling a new borehole or buying a property with an existing one, you want a yield figure before spending money on a pump. Pump systems in Johannesburg typically cost R15,000–R35,000 installed — matching the pump to actual yield avoids expensive replacements.

Water quality test: always, before drinking or cooking. If the water will touch food, skin or animals, test it. This is non-negotiable. It is also required by most municipalities if you plan to connect a borehole to an internal plumbing system that could cross-connect with municipal supply.

Both together: when commissioning a new borehole. A complete borehole system in Johannesburg typically runs R40,000–R150,000, with most falling between R60,000 and R100,000 depending on depth, casing and pump specification. At that level of investment, skipping either test to save a few thousand rands is a false economy.

Wondering what a complete borehole system would cost for your specific property and usage? Compare 3 free quotes — vetted installers, no obligation.

What about existing boreholes

If you are moving into a property that already has a borehole, treat both tests as due diligence before relying on it.

Yield can change. If the previous owner used a pump that was too large, or if the local water table has dropped due to drought or over-abstraction by neighbouring users, the sustainable yield may be lower than it was. A short pump test gives you a current baseline.

Water quality definitely needs retesting. You have no way of knowing when the previous owner last tested, whether casing seals are intact, or whether land use nearby has changed. South Africa’s groundwater resources are managed under the National Water Act, and the groundwater data portal at the Department of Water and Sanitation provides context on local aquifer conditions — but site-specific quality must come from a lab test of your actual water.

A note on borehole pump tests and broader water challenges

Johannesburg Water reports non-revenue water (losses in the reticulation network) of 44.8% based on 2024/25 audited figures, and the city’s reservoir system holds roughly 27 hours of citywide storage buffer. Those numbers explain why many homeowners are looking at boreholes as a supplementary supply. But a borehole only solves a problem if it has adequate yield and acceptable water quality — which is exactly what these two tests confirm.

If your yield is marginal, a backup tank-and-pump system (typically R20,000–R40,000 for a standard residential setup, or around R55,000 for whole-house coverage) may complement rather than replace municipal supply. In that scenario, you are still drinking municipal water and using borehole water for irrigation or toilet flushing, which changes what water quality parameters matter most.

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The short checklist

Before you use a borehole for any purpose:

• Get a yield test — confirm the borehole can supply your required daily volume without over-stressing the aquifer
• Get a water quality test — use a SANAS-accredited laboratory and test against SANS 241 parameters if potable use is intended
• Match your pump to the yield figure — not to the maximum possible extraction rate
• Set a retesting schedule — quality tests annually as a minimum, more frequently if you notice changes in taste, colour or odour
• Keep your test records — you will need them if you sell the property or apply for a water use licence

Neither test is complicated. Together they tell you what a borehole is actually worth before you depend on it.