Nitrates in Borehole Water: Testing and Treatment

Nitrates are one of the quieter risks in private water supply. You cannot taste them, smell them or see them, and a borehole that looks and smells perfectly fine can carry concentrations well above safe limits. For most healthy adults this matters less; for bottle-fed infants it can matter a great deal. If your household draws from a borehole — or is thinking about doing so — understanding nitrates, where they come from, and what to do about them is a sensible first step.

Why Johannesburg boreholes are at particular risk

Gauteng sits in a heavily developed landscape. Decades of urban expansion, agriculture on the Highveld periphery, informal settlements with limited sanitation, and suburban garden fertilising have all deposited nitrogen compounds into the soil. When rain infiltrates the ground, it carries nitrates downward into the shallow aquifers that most domestic boreholes tap.

Older residential areas with ageing sewer infrastructure are a specific concern: slow leaks from sewer lines can elevate nitrate levels in nearby groundwater. So can any property that historically kept livestock or used nitrogen-heavy fertilisers. Depth helps — deeper aquifers are generally more protected — but depth alone is not a guarantee, and Johannesburg’s geology varies considerably across suburbs.

Johannesburg Water’s own network loses roughly 44.8% of treated water as non-revenue water (2024/25 audited figures), which contributes to localised ground saturation from pipe leaks and adds to the general pressure on groundwater quality across the city.

What the standard actually says

SANS 241 is South Africa’s national drinking-water quality standard, published by the South African Bureau of Standards (SABS). The 2024 edition sets the limit for nitrate (expressed as NO₃⁻) at 11 mg/ℓ as nitrogen, which aligns with World Health Organization guidance. This is the benchmark your water should be tested against.

It is worth understanding what the standard covers and what it does not. SANS 241 applies to municipal water supplied to consumers; it does not automatically regulate private borehole water. There is no legal authority routinely testing your borehole on your behalf. That responsibility sits with you as the owner.

Why infants are the priority concern

The condition most associated with elevated nitrate exposure in very young infants is methaemoglobinaemia — sometimes called blue-baby syndrome — where nitrates interfere with the blood’s ability to carry oxygen. The National Institute for Communicable Diseases (NICD) recognises this as a clinical concern in South Africa, particularly in areas where borehole water is used to prepare infant formula without prior testing.

Healthy adults and older children process nitrates more readily, though long-term exposure at elevated concentrations is an active area of research. The conservative, practical position is: if there is any infant in the household, test before use, and do not use untreated borehole water for formula preparation until results confirm it is within the SANS 241 limit.

This article does not constitute medical advice. If you have health concerns related to water quality, consult a registered medical practitioner.

How nitrate testing works

Home testing strips exist and are widely sold, but they are not reliable enough for a safety decision. For nitrates specifically, you need an accredited laboratory analysis — a water sample collected in a clean, lab-supplied container, kept cool, and delivered within the required holding time (typically 24–48 hours for nitrate samples).

For a detailed look at the process and what to budget, the article on borehole water testing costs covers accredited lab options, typical turnaround times and what a full potability panel includes alongside nitrate analysis. A basic nitrate-only test is cheaper than a full panel, but most specialists recommend testing for the broader range of parameters at least once, since nitrate contamination often accompanies other indicators of agricultural or sewage-related ingress.

For a broader overview of what borehole water quality decisions involve — from initial drilling through to ongoing management — the borehole drilling guide is a useful reference point.

If you're at the stage of deciding whether to install a borehole or upgrade an existing one, getting specialist input early saves money. Compare 3 free quotes — vetted installers, no obligation.

Which treatments actually remove nitrates

This is where the “test first, treat second” principle becomes practical. Nitrates are not removed by standard carbon filters, sediment filters or UV sterilisation. The two treatment methods with demonstrated effectiveness are:

Reverse osmosis (RO) forces water through a semi-permeable membrane under pressure, rejecting nitrates along with a broad range of other dissolved contaminants. Point-of-use RO units fitted under a kitchen sink are the most common domestic application. They produce treated water at a relatively slow rate and generate a waste-water stream (typically two to four litres rejected per litre of product water, though this varies by unit and feed-water quality). RO is well-suited for drinking and cooking water, and for preparing infant formula. As a rough guide, a quality under-sink RO unit installed typically costs somewhere in the range of R8,000–R18,000, but confirm this via quotes from installers as pricing varies.

Ion exchange (anion exchange) uses a resin bed that selectively removes nitrate ions from water, replacing them with chloride. It can treat higher flow rates than point-of-use RO and is used where whole-house treatment is needed. Resin beds require periodic regeneration with salt solution. Sizing depends heavily on your actual nitrate concentration and daily water demand — both numbers that only a test can give you.

Method	Removes nitrates?	Treats whole house?	Ongoing maintenance
Carbon/sediment filter	No	—	Low
UV sterilisation	No	Yes	Lamp replacement
Reverse osmosis (point-of-use)	Yes	No (drinking/cooking only)	Filter and membrane changes
Anion ion exchange	Yes	Yes (with correct sizing)	Resin regeneration, salt
Distillation	Yes	No (low output)	Cleaning, energy cost

Distillation is sometimes mentioned as an option; it does remove nitrates effectively but is slow, energy-intensive and generally impractical as a primary household treatment.

The broader safety picture for borehole users

Nitrates are one parameter among many. The article is borehole water safe to drink? covers the wider set of concerns — bacteria, pH, hardness, heavy metals — that a full potability assessment should address. Treating for nitrates alone on a borehole that also has microbiological contamination does not make the water safe; it only addresses one risk.

The practical sequence most water specialists recommend: drill and case the borehole correctly, test comprehensively before first use, identify all parameters outside SANS 241 limits, then design a treatment system that addresses the actual profile of your water. Installing treatment before testing is a common and avoidable mistake.

Knowing your nitrate result before choosing a treatment system is the difference between a solution that works and one that misses the problem entirely. Get matched with a vetted water specialist — no obligation, three quotes for comparison.

Ongoing monitoring

Borehole water quality is not static. A borehole that tests clean in one season may show elevated nitrates after a wet summer if nearby agricultural activity increases, or if local infrastructure deteriorates. Most specialists suggest retesting annually as a minimum, and after any significant local land-use change nearby. Keep records of your results — they are useful if you ever suspect a change in quality, and they add demonstrable value if you sell the property.