Methodology and sources

Municipal water bills

Domestic water and sewage tariffs for 2026/27, valid from 1 July 2026, from each metro's own tariff documents: City of Cape Town budget annexures 6-55 and 6-60 (water and sanitation, no restrictions); Johannesburg Water tariffs 2026/27; City of Tshwane tariff notice 2026/27; eThekwini final tariff tables 2026/27. Cape Town and eThekwini publish rates including VAT; for Johannesburg and Tshwane we add 15 % VAT to the published rates.

A borehole saving is the difference between the variable monthly charges for the household's total use and for the total minus the borehole water. Fixed charges, levies and indigent allowances are not included.

Garden water

Monthly irrigation need of a lawn from ERA5 daily reference evapotranspiration (ET0) and rainfall for each metro, 2021–2025 (Open-Meteo archive): 0.7 × ET0 minus 75 % of rainfall, not below zero, averaged over the five years. The factor 0.7 follows FAO-56 guidance for warm-season turf.

Borehole cost and running cost

Drilling at R1 000 per metre including casing: the middle of the per-metre prices owners reported paying or being quoted on the MyBroadband forum (R500 to R1 375 per metre, 2018–2024); the Borehole Water Association's published estimate is R600 to R900 per metre before casing and other costs. Pump R20 000, 5 000 l tank R5 000, plumbing and electrics R8 000, water test R1 500 and upkeep R1 000 a year are our allowances from reported prices. Pump electricity: the energy to lift each kilolitre from the borehole depth plus 30 m of pressure head, at 40 % pump efficiency and R3.50 per kWh.

Payback

Years = cost of borehole, pump, tank and plumbing ÷ (municipal water and use-based sewage charges the garden water would add each month, minus pump electricity and upkeep). Indoor use stays on municipal water.

Rainwater tanks

A day-by-day simulation over 2021–2025 with the same ERA5 rain and reference evapotranspiration as the garden model. Rain on a 150 m² roof, 80 % of it collected, fills the tank up to its size. The lawn uses 0.7 × ET0 a day; it draws first on rain held in the soil (75 % of the rain, up to 40 mm), then on the tank, then on municipal water. With this soil store the yearly garden need is within 4 % of the monthly balance used elsewhere on the site. The rand saved is the difference in the monthly water and sewage bill at 2026/27 tariffs, with 15 kl a month of indoor use.

Sources

• City of Cape Town, Budget 2026/27 annexures 6-55 and 6-60; Johannesburg Water tariffs 2026/27; City of Tshwane tariff notice 2026/27; eThekwini final tariff tables 2026/27.
• National Water Act 36 of 1998, Schedule 1 (permissible use).
• ERA5 reanalysis via the Open-Meteo historical weather archive.
• MyBroadband forum threads on boreholes and wellpoints (11 threads, 656 posts).