The lesson of Day Zero
Cape Town's 2017-18 drought put numbers on the risk: Level 6B restrictions cut commercial users by 45%, and "Day Zero" — the point at which dams reached 13.5% and taps would have closed in favour of collection points — was averted by weeks, not years. Since then, water-shedding and multi-day outages elsewhere have made the same point repeatedly: a business that needs water every day needs more than one way to get it. The engineering questions are how much to store, which alternative source fits, and what treatment each source demands.
Stored municipal water: the first and best backup
The standard backup is simply municipal water, stored. South African municipal by-laws put a number on it for premises that require continuous supply: storage of not less than 24 hours of demand in urban areas and 48 hours in rural areas (the wording appears in the standard municipal water by-law template, e.g. Drakenstein's 2023 by-law). Feed the tank through an air gap or approved backflow preventer, and treat the tank as part of the water system, not a passive bucket: SANS 241's current edition brings static tanks into the monitoring regime, with regular testing and a cleaning programme expected. Opaque tanks, screened vents and turnover (so the contents refresh rather than stagnate) are established good practice; where water stands for days, re-dose chlorine — the WHO criterion of 0.5 mg/L free chlorine with 30 minutes of contact below pH 8 is the working benchmark — or place a UV barrier where the tank feeds the building.
Boreholes: licensed, tested, then treated
Groundwater supplies roughly 15% of South Africa's water use from over a million boreholes, and for many businesses a borehole is the only backup that adds genuinely independent supply. Two things before the drilling rig arrives: the legal position — small-scale use falls under general authorisation with registration required above 10 m³/day, larger use needs a licence, and municipal by-laws add their own registration and metering requirements — and a full laboratory analysis, because groundwater chemistry is invisible and regional.
The published South African groundwater picture names the usual suspects: iron and manganese (staining, taste and fouling — the SANS 241 aesthetic limits are 0.3 and 0.1 mg/L respectively), hardness, nitrate in a band across the Northern Cape, North West and Limpopo (the acute health limit is 11 mg/L as N), fluoride in several regions (limit 1.5 mg/L), and salinity. Each maps to a treatment answer: oxidation plus catalytic media filtration for iron and manganese, softening for hardness, anion exchange for nitrate, and reverse osmosis once TDS approaches the 1 000 mg/L mark — the threshold at which SANS 241's own definitions treat water as a desalination candidate. A borehole used for anything potable finishes with disinfection, and the whole train is verified by testing, not assumed from the first analysis — boreholes drift with seasons and abstraction.
Rainwater: free water, not clean water
Harvested roof water feels clean and routinely is not: South African tank-water studies have found E. coli and opportunistic pathogens in a large share of samples. For irrigation, washdown and toilets, coarse filtration and first-flush diversion suffice — with the plumbing separated from the potable system (backflow prevention where any interconnection exists, and "do not drink" signage on non-potable lines, per the published municipal guidelines for alternative water installations). Making rainwater drinkable is a treatment project like any other: first-flush diversion, sediment filtration, carbon, and UV or chlorination — designed to the same endpoint every alternative source must meet, which is SANS 241 at the point of use. That endpoint, incidentally, is exactly what the municipal guidelines require of any alternative source used for drinking or food preparation.
Rule of thumb
Store a day or two of demand as the first layer; add a borehole where the business case justifies independent supply, and budget for its treatment train from the analysis, not the brochure. Whatever the source — tank, borehole, rain or tanker — the destination is the same: SANS 241 water at the point of use, with a disinfection barrier last and test results to prove it.