Data · garden water
How much water does a garden need in Cape Town, Joburg, Pretoria and Durban?
How much water a borehole saves depends on how much your garden would otherwise drink from the tap. We calculated it month by month from five years of weather in each metro.
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 rainfall, 2021–2025
- A warm-season lawn needs 730 mm of irrigation a year in Pretoria, 672 mm in Johannesburg, 597 mm in Cape Town and only 314 mm in Durban.
- For a 250 m² garden that is about 182 kl a year in Pretoria and 79 kl in Durban: the difference between a borehole that pays and one that does not.
- The seasons are opposite: Cape Town gardens need most water in Jan, during the dry summer; Gauteng gardens in Sep, at the end of the dry winter.
- In Gauteng the peak garden months fall before the summer rains, so a borehole earns most of its saving from August to October.
| Tshwane (Pretoria) | 730 mm |
| Johannesburg | 672 mm |
| Cape Town | 597 mm |
| eThekwini (Durban) | 314 mm |
Average 2021–2025. 1 mm on 1 m² is 1 litre; 1 mm on 250 m² is a quarter of a kilolitre.
Irrigation need by month, mm
| Metro | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Cape Town | 115 | 96 | 46 | 32 | 7 | 0 | 0 | 0 | 34 | 75 | 94 | 97 | 597 |
| Johannesburg | 37 | 25 | 54 | 37 | 55 | 51 | 66 | 84 | 100 | 86 | 48 | 27 | 672 |
| Tshwane (Pretoria) | 42 | 30 | 65 | 40 | 62 | 59 | 70 | 89 | 101 | 86 | 50 | 34 | 730 |
| eThekwini (Durban) | 10 | 26 | 12 | 19 | 28 | 35 | 54 | 53 | 19 | 13 | 35 | 11 | 314 |
Need = 0.7 × reference evapotranspiration − 75 % of rainfall, per month, not below zero; average of 2021–2025. Multiply by the garden area in m² and divide by 1 000 for kilolitres.
Lawn, beds and indigenous plants
The factor 0.7 is for a well-kept warm-season lawn such as kikuyu or buffalo grass. Beds with established shrubs need less, and an indigenous, water-wise garden much less. If half your garden is paving or indigenous planting, count only the lawn and thirsty beds in the calculator.
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.