Borehole Testing
Cape Town

Borehole testing answers one question, and only one: how much water can this borehole reliably deliver, and for how long, without being over-pumped?

It is worth separating that question from the ones around it. Testing does not tell you whether the water is drinkable - that is water quality testing, an entirely different exercise on a laboratory bench. Testing here means yield testing: controlled pumping with measurement, to establish what the borehole can sustain.

It is also the step most often skipped, usually to save time before a pump goes in. Skipping it is a false economy, because everything downstream depends on the result.

Why the Drilling Air-Lift Figure Is Not a Yield

During drilling, compressed air lifts water out of the hole and the driller notes an apparent flow. This "blow yield" is genuinely useful - it tells you a water strike occurred and gives a rough sense of scale. It is not a yield figure you should size a pump on, for several reasons:

• It is measured over minutes, not hours, so it says nothing about whether the flow is sustainable
• It reflects conditions during drilling, with the formation disturbed and drilling water in the system
• It gives no information about how far the water level draws down under sustained abstraction
• It gives no information about how quickly the borehole recovers afterwards
• It is an estimate by observation rather than a calibrated measurement

A borehole that blows strongly for ten minutes may sustain only a fraction of that over eight hours. The difference between those two numbers is exactly what a yield test exists to establish.

What a Yield Test Involves

A proper test is a sequence of controlled pumping stages with continuous measurement of water level, flow rate and time. In practice it runs like this:

1. 1Measure the standing water level - the rest level before any pumping, established after the borehole has been undisturbed.
2. 2Install a test pump and a calibrated flow measurement arrangement, with a dip meter or logger to track water level.
3. 3Run a step-drawdown test. The borehole is pumped at several increasing rates, each for a set period, recording how far the level falls at each step. This shows how the borehole responds as abstraction increases and helps identify the rate at which drawdown becomes excessive.
4. 4Allow recovery between the step test and the main test so the level returns toward rest.
5. 5Run a constant discharge test. The borehole is pumped at a single steady rate for an extended period, with water level recorded at intervals that are close together at first and further apart later. This is the core of the test.
6. 6Monitor recovery. When pumping stops, the rate at which the level rises back toward rest is recorded. Recovery behaviour says a great deal about the formation and about long-term sustainability.
7. 7Take a water sample during the constant-rate test, when the borehole has been pumping long enough to be drawing formation water rather than water standing in the casing.
8. 8Analyse and report, converting the raw data into a recommended sustainable abstraction rate with the pumping level and recommended pump setting depth.

Test duration varies with the borehole and the intended use. A domestic garden supply does not need the same test programme as an irrigation borehole that will run for hours daily, and the test should be scoped to the use.

What the Results Actually Tell You

Measurement	What it means and what it is used for
Standing water level	Depth to water at rest. The baseline against which drawdown is measured, and a reference for future monitoring.
Drawdown	How far the water level falls below rest while pumping at a given rate. Modest drawdown at a good flow indicates a productive borehole; steep drawdown at a low flow indicates a tight one.
Pumping water level	Where the level settles under sustained abstraction. This is the figure that determines the total head a pump must overcome, and how deep the pump must be set.
Specific capacity	Yield per unit of drawdown - a comparative measure of borehole performance, and a useful baseline for spotting deterioration years later.
Recovery rate	How quickly the level returns after pumping stops. Slow recovery suggests the formation replenishes slowly, which constrains how the borehole can be used through the day.
Sustainable abstraction rate	The recommended rate the borehole can support on an ongoing basis, usually with a recommended daily running duration. The single most important output of the test.

Why Testing Comes Before Pump Selection

The chain is straightforward. The test gives you a sustainable rate and a pumping water level. The pumping level, plus lift, friction and any required outlet pressure, gives the total head. Rate and head together define the duty point, and the duty point selects the pump.

Fit a pump without that data and one of two things generally happens. Either the pump is too large, in which case it out-draws the borehole, runs the level down to the intake and eventually damages itself. Or it is too small, in which case you have paid for a borehole you are not using properly. Both are avoidable for the cost of a test.

The pump installation page covers how the duty point translates into a specific pump.

Testing an Existing Borehole

Yield testing is not only for new boreholes. It is the right diagnostic step when an established borehole is underperforming:

• Flow has dropped noticeably compared with previous years
• The pump cuts out on dry-run protection during normal use
• Water runs strongly at first and falls away after a period of running
• You are considering a larger pump and want to know whether the borehole can support one
• Demand on the property has increased and you need to know whether the borehole can carry it
• You are buying a property with an existing borehole and want to know what you are actually getting

Re-testing an existing borehole against its original figures is the clearest way to distinguish a declining borehole from a failing pump. If the borehole still tests at close to its original specific capacity, the problem is in the equipment and belongs on the repairs page. If the borehole itself has deteriorated, rehabilitation may be the appropriate route.

What Affects Testing Cost

Factor	Why it matters
Test duration and programme	A short domestic test is a different scope from an extended constant-rate test for an irrigation or commercial supply.
Borehole depth and expected yield	Deeper boreholes and higher rates need larger test pumps and generators.
Site access and power	Whether mains power is available or a generator must be brought in and fuelled for the test duration.
Water disposal	Test pumping discharges a substantial volume that has to go somewhere sensible, away from the borehole so it does not recirculate.
Data logging	Manual dip readings versus continuous electronic logging, which gives finer resolution and a better record.
Reporting depth	A basic yield figure versus a full report with analysis, recommended abstraction regime and pump setting recommendations.
Sampling	Whether a water sample is taken during the test for separate laboratory analysis.

Set against the cost of an unsuitable pump - plus the borehole damage that over-pumping can cause - testing is usually one of the better-value items in a borehole project.

Related Borehole Services

Yield testing is the step between drilling and installation, so it makes most sense alongside the rest of the sequence - Borehole Drilling Cape Town sets out what happens before the test and why the air-lift figure noted during drilling is not the yield.

What Borehole Yield Testing Costs

Set this against the cost of getting pump selection wrong. An oversized pump on an untested borehole runs the water level down to the intake and fails early, which costs more than the test would have.

Item	Indicative range	What moves it
Basic yield check, domestic	R3,500 – R7,000	Short programme suitable for a garden supply on a modest borehole.
Step-drawdown plus constant discharge test	R6,000 – R15,000	The full programme with recovery monitoring. Duration, test pump size and whether a generator is needed.
Extended test, commercial or agricultural	R15,000 – R40,000+	Longer constant-rate runs for sustained abstraction, plus data logging.
Test report with recommended abstraction regime	Usually included	Confirm you receive specific capacity and a recommended pump setting depth, not just a flow figure.
Water sample taken during the test	R1,200 – R3,500	Laboratory analysis is charged separately - see water testing.

Borehole Yield Testing FAQs

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