Explainer

Borehole water in the Cape Winelands: testing and treatment

The contaminants most often found in Winelands boreholes, how SANS 241 testing works, and how treatment is matched to your results.

By Niel Swart, Founder, Skoon Water · Published 5 October 2026

Farms, wine estates and smallholdings across the Cape Winelands rely on boreholes, and municipalities use groundwater too. In February 2026 Stellenbosch Municipality said it was bringing back boreholes it had used during the 2018 drought to supplement supply (Stellenbosch Municipality, 6 February 2026).

Unlike municipal water, your private borehole water isn't treated or tested unless you arrange it. The City of Cape Town warns that groundwater quality is unpredictable, changes over time and can vary hugely even within one property (City of Cape Town, *The risks of groundwater quality*, 2019). This guide covers the contaminants most likely to matter, how SANS 241 testing works, and how treatment is matched to the results.

Why borehole water varies across the Winelands

Geology is a big part of it. In the coastal wine region around Stellenbosch and Paarl, the oldest rocks are the largely shaley Malmesbury Group. Granites of the Cape Granite Suite underlie many Stellenbosch and Paarl vineyards, and resistant Table Mountain Group sandstones form ridges such as the Hottentots-Holland and the Stellenboschberg (Bargmann, *An overview of geological influences on South African vineyards*).

City of Cape Town guidance notes that less permeable rocks such as shale generally tend to have very poor water quality, while fractured sandstones usually have better quality and deeper boreholes generally give better water. Agriculture, landfill sites and waste dumping can also affect groundwater (City of Cape Town, 2019).

None of this predicts what's in your borehole, which is why testing comes first.

Common borehole contaminants in the Cape Winelands

The limits below come from SANS 241-1:2015, as published by Vinlab in Stellenbosch and GEOSS. SANS 241 has since been revised (see the testing section below), so check which edition your lab report uses.

Iron

What you notice: water that comes out clear but turns reddish-brown after standing, a metallic taste, and rust-coloured stains on basins, laundry and walls. A 2004 City of Cape Town aquifer study puts iron's taste threshold at about 0.3 mg/L and says staining starts above about 0.2 mg/L (TMG Aquifer Alliance for the City of Cape Town, 2004).

Why it matters here: the same study calls iron biofouling a widespread problem in the Western and Eastern Cape. Iron deposits and bacterial slime build up and can clog borehole screens, pumps and pipes. Iron problems are common in Table Mountain Group aquifers, and Malmesbury Group groundwater is also commonly affected.

SANS 241-1:2015 limit: 0.3 mg/L (aesthetic) and 2 mg/L (chronic health). The Water Research Commission's (WRC) domestic water guide notes that at the levels normally found in water, iron causes aesthetic rather than toxic effects (WRC TT 101/98, *Quality of Domestic Water Supplies, Vol. 1*).

Manganese

What you notice: brown or black staining of laundry and fittings, darker water and sometimes a metallic taste (WRC TT 101/98). The WRC guide also notes that the tea-coloured water of the Southern and Western Cape is due to organic material together with manganese.

SANS 241-1:2015 limit: 0.1 mg/L (aesthetic) and 0.4 mg/L (chronic health).

Hardness (calcium and magnesium)

What you notice: white scale in kettles, geysers and shower heads, and soap that won't lather well. Hardness is the combined calcium and magnesium content, reported as mg/L calcium carbonate (CaCO₃). The WRC guide classes 50–100 mg/L as moderately soft, 200–300 mg/L as hard and 300–600 mg/L as very hard, with some kettle scaling starting from about 100–150 mg/L (WRC TT 101/98).

Health: the WRC guide says some hardness is beneficial because it supplies calcium and magnesium, though very hard water should be avoided by some sensitive groups. Very soft water causes problems too: the WRC links low hardness with corrosion, and the 2004 aquifer study describes Table Mountain Group groundwater as often acidic and potentially corrosive.

SANS 241: the 2015 edition set no hardness limit. According to a former chair of the SABS water committee, the 2025 edition highlights hardness, alkalinity and calcium carbonate stability as important for preventing corrosion and pipe damage (Infrastructure News, 21 May 2026).

Bacteria: E. coli and total coliforms

What you notice: usually nothing, so only a laboratory test will find them.

Why it matters: E. coli and faecal coliforms indicate faecal contamination from humans or animals, and therefore the possible presence of germs that cause stomach illness. Infants and people with weakened immune systems are most at risk (WRC TT 101/98). Total coliforms indicate the general hygienic quality of the water. The City of Cape Town lists sewer leaks, pit latrines and stagnant ponds or wetlands among the possible sources of groundwater contamination (City of Cape Town, 2019).

SANS 241-1:2015 limits: E. coli or faecal coliforms must not be detected in 100 mL. Total coliforms must be no more than 10 per 100 mL (an operational limit).

Nitrate

What you notice: nothing. The WRC guide notes that nitrate has no taste, colour or smell. It says nitrate comes from decaying plant, animal and human waste, and that nitrate-nitrogen above 20 mg/L is common in groundwater wherever land use is intensive. The main risk is to babies under one year old (WRC TT 101/98).

SANS 241-1:2015 limit: 11 mg/L as N (acute health).

Salinity, sodium, chloride and sulphate

SANS 241-1:2015 sets aesthetic limits of 170 mS/m for electrical conductivity, 200 mg/L for sodium and 300 mg/L for chloride. Sulphate has an aesthetic limit of 250 mg/L and an acute health limit of 500 mg/L.

SANS 241 testing for your borehole

SANS 241 is South Africa's national drinking water standard. The current edition, SANS 241:2025, was approved on 28 November 2025 and replaces SANS 241-1 and SANS 241-2 of 2015 (SABS). Committee members say the new edition is risk-based, E. coli remains the main microbiological indicator, and turbidity must now be at or below 1 NTU (Infrastructure News, 18 August 2026).

For a private borehole, practical guidance is:

Test against the full SANS 241 standard at a SANAS-accredited laboratory. This is the City of Cape Town's advice to groundwater users (City of Cape Town, 2019).
Test both microbiological and chemical parameters. Iron and staining are visible. E. coli and nitrate aren't.
Test regularly, not once. "What tested fine last month may be different today," the City of Cape Town notes. Retest after installing treatment, after flooding or nearby construction, and whenever taste, colour or smell changes.
A useful benchmark: under SANS 241:2025, small community borehole systems serving up to 5,000 people need a full analysis every second year and a reduced set of tests twice a year (Infrastructure News, 21 May 2026). That rule doesn't apply to private households.

In the City of Cape Town, which includes the Northern Suburbs, the City's Water By-law says groundwater may not be used for drinking, cooking, food preparation or body washing, whether treated or not, except by some large consumers contracted with the City under strict conditions. A reduced pressure zone (RPZ) backflow valve is mandatory if groundwater is connected to your plumbing (City of Cape Town, 2019). Elsewhere in the Winelands, check the rules with your municipality before connecting borehole water to household taps.

Treatment options, matched to your results

Treatment should follow the test, not the other way round. Common building blocks are:

Sediment pre-filtration removes sand, silt and particles. It protects the treatment stages after it, and disinfection works better in clear water than in cloudy water (WRC TT 101/98).
Iron and manganese removal. Dissolved iron and manganese are oxidised with air or a chemical oxidant such as chlorine, then the particles that form are filtered out (WRC TT 101/98; TMG Aquifer Alliance, 2004). pH matters: the 2004 study notes that dissolved iron oxidises quickly only above about pH 7, so acidic water may need pH correction first. Iron or manganese bound to organic matter is harder to remove.
Softening for hardness. The WRC guide lists cation-exchange softening as a treatment for hardness. See water softeners and water filtration versus water softening.
Disinfection for bacteria. The WRC guide says full removal of coliform bacteria needs effective disinfection, using chlorine or physical methods such as ultrafiltration or UV light. UV purification is usually installed after filtration, because UV needs clear water to work.
Reverse osmosis or ion exchange for nitrate and salts. The WRC guide lists ion exchange and reverse osmosis among the methods for removing nitrate. Reverse osmosis is usually installed at the kitchen tap for drinking and cooking water.

A borehole system often combines several of these stages, sized to your flow rate. After installation, retest to confirm it works, and keep up with servicing: filters, UV lamps and media need replacing over time. If you also have municipal water, see Is Stellenbosch tap water safe to drink?

Get your borehole water tested

Not sure what's in your borehole? Book a water test or assessment, or book our SANS 241 chemical and microbiological water analysis, which includes on-site sample collection and laboratory delivery within our 25 km service radius. Once you have results, we'll design borehole filtration around them. We work across the Winelands, from Stellenbosch to Paarl and Franschhoek.

Frequently asked questions

Is borehole water safe to drink without treatment?

You can't assume it is. Groundwater quality varies between boreholes and changes over time, and bacteria such as E. coli and chemicals such as nitrate can't be seen or tasted. Have it tested against SANS 241 at an accredited laboratory before you drink it.

How often should I test my borehole water?

Regularly, not just once. The City of Cape Town notes that groundwater that tested fine last month may be different today. Retest after installing treatment, after floods or nearby construction, and whenever the taste, colour or smell changes.

What does a SANS 241 water test check?

SANS 241 covers microbiological parameters such as E. coli and total coliforms, plus physical and chemical parameters such as turbidity, pH, conductivity, iron, manganese, nitrate and other metals. Ask your laboratory which edition it reports against.

Why does my borehole water stain basins and laundry brown or black?

Reddish-brown stains usually point to iron, and brown or black stains to manganese. Iron problems are common in Western Cape groundwater. A test confirms the levels, and oxidation followed by filtration is the usual treatment for both.

Can a filter remove E. coli from borehole water?

Bacteria need disinfection, not just filtration. The WRC lists chlorine, ultrafiltration and UV light as options. UV works best after pre-filtration has removed particles, and you should retest after installation to confirm the system works.

Is hard borehole water bad for my health?

Usually not. The WRC notes that some hardness is beneficial because it supplies calcium and magnesium, though very hard water should be avoided by some sensitive groups. The main problems are scale in kettles and geysers and poor soap lathering, which a softener can address.