Analysis · yield
How strong does your borehole need to be? Yield for your garden
A yield test tells you how many litres an hour your borehole can give. But how many do you need? We took the hottest, driest week of 2021–2025 in each metro and worked out what a lawn drinks then.
By Borehole Payback · updated 24 October 2026
Will a borehole pay for itself?
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Garden water from each metro's average 2021–2025 weather; 2026/27 water and sewage tariffs incl. VAT; pump electricity at R3.50 per kWh. Drilling at R1 000 per metre incl. casing.
What our numbers show
Our calculation from ERA5 daily evapotranspiration and rain, 2021–2025, peak 7-day average
- In the hottest dry week of the last five years a lawn in Johannesburg used 5.5 mm of water a day. For 250 m² that is 1 368 litres a day, or 228 L/h if the pump runs 6 hours.
- Even an 800 m² garden needs only 729 L/h at that peak. Watering the garden asks less of a borehole than many owners expect; adding a household's indoor use of about 500 litres a day lifts a 250 m² garden to 311 L/h.
- Durban's peak is the lowest at 4.1 mm a day: summer rain keeps the soil wet, which is also why a borehole there replaces less municipal water.
- The figure that matters is the sustainable yield from a proper pump test, not the flow on the day the hole is drilled. A tank between borehole and garden lets a weak borehole pump slowly all day and the garden take its water in an hour.
| Johannesburg | 228 L/h | |
| Tshwane (Pretoria) | 223 L/h | |
| Cape Town | 194 L/h | |
| eThekwini (Durban) | 171 L/h |
Lawn need 0.7 × ET0 after rain held in the soil (40 mm store); pump running 6 hours a day; the single worst week of 2021–2025.
Yield you need, by metro and garden size
Litres per hour the borehole must deliver in the hottest dry week of 2021–2025, if the pump runs 6 hours a day. The last column adds about 500 litres a day of indoor use:
| Metro | Peak week, mm a day | 100 m² | 250 m² | 400 m² | 800 m² | 250 m² + house |
|---|---|---|---|---|---|---|
| Johannesburg | 5.5 | 91 L/h | 228 L/h | 365 L/h | 729 L/h | 311 L/h |
| Tshwane (Pretoria) | 5.3 | 89 L/h | 223 L/h | 357 L/h | 713 L/h | 306 L/h |
| Cape Town | 4.7 | 78 L/h | 194 L/h | 310 L/h | 620 L/h | 277 L/h |
| eThekwini (Durban) | 4.1 | 69 L/h | 171 L/h | 274 L/h | 548 L/h | 255 L/h |
Daily lawn need is 0.7 × reference evapotranspiration, after the soil has used up stored rain (75 % of rainfall, up to 40 mm). Peak = the highest 7-day average in the five years. No allowance for sprinkler losses: water lost to wind and midday evaporation comes on top.
What to ask the driller
- A pump test, not a blow yield. The air-lift flow measured while drilling can overstate what the hole gives over weeks of pumping. Ask for a test pumping of several hours with the recovery measured afterwards.
- The sustainable yield in litres per hour, and the depth the water level drops to while pumping. The pump should hang above that level.
- Water quality if you will use the water indoors: iron, hardness and bacteria decide what treatment you need.
Why a tank changes the sum
The numbers above assume the pump feeds the sprinklers directly. With a storage tank, a borehole that gives 150 litres an hour can pump for nine hours, fill the tank, and the garden can take 1 368 litres in one go. A tank lets you size the borehole for the day, not for the hour, and protects the pump from running the hole dry.
See what a borehole costs, garden water month by month and rainwater tank or borehole.
This week
Metro of the week: eThekwini (Durban)
A household in eThekwini (Durban) using 30 kl of municipal water a month pays about R2 253 a month for water and sewage under the 2026/27 tariffs. A 60 m borehole watering a 250 m² garden would save about R4 769 a year after pump electricity and upkeep, and pay back in 19.8 years.