Water pH Explained: Acidic and Alkaline Water at Home

pH is one of those water-quality numbers that sounds like school chemistry but turns out to matter quite a lot in your home. It influences whether your copper pipes are slowly dissolving into your drinking water, whether your geyser element is furring up, and whether the chlorine in municipal supply is actually doing its job. Here is what the number means, what Johannesburg water typically looks like, and when you should think about correcting it.

What the pH Scale Actually Means

The pH scale runs from 0 to 14. Pure water at 25 °C sits at 7 — neutral. Anything below 7 is acidic; anything above 7 is alkaline (also called basic). Each whole number represents a tenfold change in hydrogen-ion concentration, so pH 5 is ten times more acidic than pH 6, and a hundred times more acidic than pH 7. In practice, the drinking water you encounter at home sits somewhere between pH 6 and pH 9, which sounds like a narrow band but creates meaningfully different conditions for your plumbing and appliances.

For context, rainwater is naturally slightly acidic — typically around pH 5.5–6 — because it absorbs carbon dioxide from the atmosphere and forms weak carbonic acid. Groundwater picks up minerals as it moves through rock, which usually pushes pH upward. Municipal treatment plants add chemicals to keep pH within a controlled range before water leaves the reservoir.

What SANS 241 Requires

South Africa’s drinking-water quality standard, SANS 241 (2024 edition), sets the acceptable pH range at 5.0–9.5 for water supplied to consumers. Most utilities target a tighter operational range — broadly 6.5–8.5 — because that window keeps chlorine disinfection efficient and reduces pipe corrosion. If your tap water is tested and falls outside 5.0–9.5, it technically does not meet the standard.

Water sitting below pH 6.5 becomes progressively more corrosive to metal pipework. Water sitting above pH 8.5 starts to reduce how effectively free chlorine disinfects. Neither extreme is ideal, and both can occur at the household level even when the treatment works sends water out at the correct pH — because the water changes as it travels through kilometres of ageing reticulation.

How pH Affects Your Pipes and Appliances

This is where pH stops being abstract and starts costing you money.

Acidic water (below ~6.5): Low-pH water is corrosive to copper, galvanised steel, and certain fittings. Over time it leaches copper ions from pipes, turning water bluish-green and leaving blue-green stains on basins and baths. It can also dissolve lead from older solder joints — a genuine health concern. Acidic water shortens the life of geysers and hot-water systems.

Alkaline water (above ~8.5): High-pH water tends to carry more dissolved calcium and magnesium, which precipitate out as scale when water is heated. Scale coats geyser elements, reduces their efficiency, and eventually causes them to fail prematurely. High pH also reduces the germicidal punch of chlorine, which matters if your water is stored in tanks before use.

The sweet spot for most homes is roughly pH 7–8. At that range, a thin protective carbonate layer forms on the inside of pipes (called a passivation layer), corrosion slows dramatically, and chlorine remains effective.

Johannesburg’s municipal supply generally falls within an acceptable range when it leaves the treatment works, but Johannesburg Water’s own audited figures show non-revenue water of 44.8% — meaning a large portion of treated water leaks or is otherwise lost in the distribution network. Ageing, cracked pipes in that network can allow pH to drift by the time water reaches your tap, and borehole water in Gauteng varies widely depending on the geology of your stand.

How to Find Out Your Water’s pH

There are a few options, ranging from rough to precise:

• pH test strips are cheap and available at pool-supply shops. They give a broad reading — good enough to flag a serious problem, not accurate enough for treatment decisions.
• Handheld pH meters cost more but give readings to one decimal place. They need calibration fluid and a bit of care.
• Laboratory water tests are the only approach worth relying on if you are planning treatment. A proper test panel covers pH alongside hardness, metals, microbiology, and other SANS 241 parameters. Once you have results in hand, reading a water test report explains how to interpret the numbers without needing a chemistry degree.

If you are on borehole water, a lab test is non-negotiable before you decide on any filtration or treatment system. Municipal water is generally tested by Johannesburg Water, but your on-site results can still differ.

Unsure which pH-correction or filtration system suits your water? Compare 3 free quotes — vetted installers, no obligation.

Treatment Options for Acidic or Alkaline Water

Once you know your pH, correction is usually straightforward. The right approach depends on how far outside range your water sits and what else the test reveals.

Problem	Common treatment	Notes
Mildly acidic (pH 6.0–6.5)	Calcite (calcium carbonate) filter	Raises pH gradually; also adds slight hardness
Moderately acidic (pH < 6.0)	Calcite/magnesium oxide blend or chemical dosing	Stronger correction; requires sizing by installer
Alkaline with scaling (pH > 8.5)	Acid dosing, softener, or scale-inhibition filter	Choice depends on hardness levels too
Borehole with variable pH	Whole-house filtration with pH correction stage	Often combined with sediment and UV disinfection

Calcite filters are the most common residential fix for acidic borehole water in Johannesburg. They are passive, require periodic topping up with media, and are relatively low-maintenance. Chemical dosing systems (which inject a small amount of soda ash or similar) are more precise but add ongoing chemical costs.

For a broader picture of what treatment options exist and how they fit together, the water filtration guide covers the full range of technologies available to South African homeowners.

As a rough guide, a standalone pH-correction filter stage typically adds R5,000–R15,000 to a system installation, though you should confirm exact costs via quotes because pricing varies with flow-rate requirements and what other treatment stages are included.

pH and Drinking Safety: What the Research Says

PH within the SANS 241 range is not directly toxic. The concern is indirect: low pH mobilises metals from pipes (copper, lead) into drinking water, and it is those metals that create health risk with long-term exposure. High pH is not itself harmful to drink, but it signals water chemistry that may cause other problems.

If you are on borehole water, the National Institute for Communicable Diseases (NICD) is consistent in its guidance that private water supplies should be tested and treated before use for drinking — pH correction alone is rarely sufficient; microbial safety must also be confirmed. The South African Bureau of Standards (SABS) administers SANS 241, which provides the testing framework.

Ready to get your water properly assessed and treated? Get quotes from certified local installers — free comparison, no obligation.

Putting It Together: A Practical Checklist

If you have read this far and are wondering what to do next, here is a straightforward sequence:

1. Get a lab water test — not just pH, but a full panel including metals and microbiology. On municipal supply, test at the tap. On borehole, test the raw borehole water.
2. Identify the problem — is pH the only issue, or does the test reveal hardness, iron, or microbial concerns that need addressing simultaneously?
3. Get multiple quotes for treatment — the technology choice and the price vary considerably between installers. Understanding how to compare water quotes will help you read proposals critically rather than just comparing headline prices.
4. Confirm sizing — a pH-correction filter sized for a small flat will not cope with a four-bathroom house on borehole supply. Installers should specify flow rate and media volume, not just product brand.
5. Plan maintenance — calcite media needs periodic topping up; chemical dosing systems need reagent replenishment. Factor running costs into your decision.

Getting the pH right is not a luxury for chemistry enthusiasts. It is basic infrastructure protection — for your pipes, your geyser, and the water your household drinks every day.