What Is Potable Water? Definitions That Matter

You will see the word “potable” on borehole quotes, tank-and-pump proposals, and filtration brochures. It sounds technical, but the idea is straightforward: potable water is water safe enough to drink, cook with, and use for food preparation without posing a health risk. The complication is that “safe enough” is not a feeling — it is a defined legal threshold, and understanding where that line sits matters before you spend money on any water solution.

The Legal Definition: SANS 241

In South Africa, the drinking-water quality standard is SANS 241, currently in its 2024 edition and published by the South African Bureau of Standards (SABS). SANS 241 sets limits for microbiological contaminants (bacteria, protozoa, viruses), chemical parameters (nitrates, heavy metals, disinfection by-products), and physical characteristics (turbidity, colour, taste, odour). Water that meets all of those limits is, by definition, potable. Water that fails any of them is not, regardless of what it looks like.

Johannesburg Water is obliged to deliver water that complies with SANS 241 at your meter. Beyond the meter — inside your plumbing, your storage tank, or your borehole — compliance is your responsibility. This distinction is more important than most homeowners realise.

Potable vs Non-Potable: Where the Line Falls

Non-potable water is simply water that has not been confirmed to meet the SANS 241 thresholds. That covers a wide range:

• Untreated borehole water — may be clean, may contain E. coli, nitrates, or heavy metals depending on the aquifer and local geology. You cannot tell without a lab test.
• Harvested rainwater — picks up contaminants from roof surfaces and guttering; typically non-potable without treatment.
• Grey water — water already used in showers, basins, or laundry; classified non-potable and regulated separately.
• Municipal water after storage — water held in a tank without proper inlet protection or disinfection can become non-potable through bacterial regrowth.

The potable/non-potable distinction is not a permanent label on a source. It is a status that depends on current test results. A borehole can be potable one season and fail the following year if local contamination changes. This is why the principle is test first, treat second — not the other way around.

Source	Typical default status	Primary risk if untreated
Municipal supply (at meter)	Potable (SANS 241 compliant)	Post-meter contamination
Borehole	Non-potable until tested	Microbial, nitrate, heavy metals
Harvested rainwater	Non-potable	Microbial, rooftop pollutants
Grey water	Non-potable	Microbial, chemical
Stored municipal water	Depends on storage hygiene	Bacterial regrowth

Why Johannesburg Homeowners Need to Understand This

Johannesburg’s municipal system faces real pressure. Johannesburg Water’s own audited figures for 2024/25 show non-revenue water at 44.8% — a measure that includes losses from leaks, theft, and metering inaccuracies. The city’s reservoir system holds roughly 27 hours of citywide storage buffer. When outages or low-pressure events occur, homeowners draw on backup sources, and that is exactly when the potable/non-potable distinction becomes critical.

If you are considering a borehole as a backup or primary supply, the question of whether borehole water is safe to drink is answered in detail in our guide on is borehole water safe to drink. The short version: the geology of Johannesburg varies considerably, and assumption is not a substitute for a certified laboratory water test.

For broader context on treatment technologies — filtration, UV disinfection, reverse osmosis — the water filtration pillar covers how each method addresses specific contaminants and where each fits in a potable-water treatment chain.

If you're weighing up a borehole, tank system, or filtration setup and want to know what compliant installation actually costs in your area. Compare 3 free quotes — vetted installers, no obligation.

Non-Potable Water Still Has Real Uses

Non-potable water is not worthless water. It has legitimate, practical applications that can meaningfully reduce your municipal consumption:

• Toilet flushing — accounts for a significant share of household water use and requires no drinking-water quality.
• Garden irrigation — many plants tolerate water quality well below SANS 241 thresholds, though some contaminants can affect soil health over time.
• Washing vehicles and hard surfaces — no potable standard required.
• Laundry (grey water reuse) — subject to local by-law compliance; check with your municipality.

Using non-potable water for these purposes while reserving potable supply for consumption and food preparation is a sensible dual-supply approach, provided the two systems are clearly labelled and cannot cross-connect. Cross-connection — where a non-potable line can back-flow into a potable supply — is a genuine health risk and a code violation.

Who Certifies and Who Tests?

SANS 241 is the standard. The SABS sets and maintains it. But day-to-day testing is carried out by accredited laboratories — you are looking for labs with SANAS (South African National Accreditation System) accreditation for water testing. Your municipality is not the right body to test your borehole or private tank; they test the reticulation system.

For health guidance on waterborne illness and what contaminants pose which risks, the National Institute for Communicable Diseases (NICD) publishes factsheets that are worth reading before you make decisions about treatment. Their guidance is descriptive and risk-based, not a replacement for a laboratory result.

A full water quality test from an accredited lab typically covers the main SANS 241 parameters and will tell you precisely what treatment — if any — is needed. It is the only honest starting point.

What to Look for in Quotes and Proposals

When you receive proposals for any water solution that claims to deliver potable water, a few things are worth scrutinising:

1. Does the installer specify which SANS 241 parameters the treatment addresses? A UV unit handles microbial risk but does nothing for nitrates or heavy metals. A proposal that simply says “potable” without specifying the treatment chain deserves a follow-up question.
2. Is a baseline water test included or recommended? If not, ask why. Treatment should be matched to what is actually in your water.
3. What ongoing maintenance does the system require? Filter cartridges, UV lamp replacement, and periodic testing all carry costs. These should appear in the proposal.
4. Is the installer willing to provide written confirmation of the system’s output standard? Reputable installers will stand behind that claim.

Our guide on how to compare water quotes walks through the specific line items to check when you receive competing proposals, which saves time and prevents mismatched comparisons.

Ready to get real numbers from installers who work in your part of Johannesburg? Get your free installer quotes — vetted installers, no obligation.

The Practical Summary

Potable water has a precise meaning in South Africa: it meets SANS 241. That status depends on testing, not on the source or on appearances. Municipal water at your meter is designed to be potable; what happens beyond that point depends on your infrastructure. Borehole, rainwater, and stored water are non-potable by default until a certified test says otherwise. Non-potable water has legitimate uses, but keeping potable and non-potable supplies strictly separated is both a safety requirement and a code obligation. Any water solution that claims to produce potable water should specify how it addresses the relevant SANS 241 parameters — and you should have the baseline test data to confirm it is working.