Common Borehole Water Problems: Iron, Hardness, Smell

Borehole water in Johannesburg is not the same as municipal supply, and that is both its strength and its complication. You are drawing from aquifers that have their own mineral chemistry, bacterial populations and dissolved gases — none of which have been treated before the water reaches your tap. The result is that most Joburg borehole owners encounter at least one of three recurring problems: iron, hardness or smell. Understanding what causes each, and what actually fixes it, saves you from buying the wrong equipment.

Why Joburg borehole water tends to be problematic

The geology beneath Johannesburg — particularly the dolomite and granite formations common across the East Rand, West Rand and Midrand corridors — means groundwater picks up minerals as it moves through rock over long periods. Unlike surface water, it has no exposure to sunlight or oxygen until it is pumped up, which allows certain dissolved compounds to remain stable underground but behave unpredictably once they hit air. This is not a flaw unique to a poorly drilled borehole; it is simply what groundwater does. If you are planning a new installation, the full picture of what a borehole system involves is covered on our borehole drilling guide.

The only way to know exactly what is in your water is a laboratory test against SANS 241, the South African national drinking-water quality standard (2024 edition). Everything else is an educated guess.

Iron: the rust stain culprit

Iron is the most frequently reported borehole water problem in Johannesburg. It shows up in two forms. Ferrous iron is dissolved and invisible — the water looks clear when it comes out of the tap, but leaves orange or rust-brown stains on basins, toilets and laundry once it oxidises on contact with air. Ferric iron is already oxidised and makes the water visibly orange or brown straight from the tap.

A third form, iron bacteria, is less common but worth knowing about. These are naturally occurring bacteria that feed on dissolved iron and produce a slimy, rust-coloured residue that can foul pipes, tanks and irrigation lines.

Treatments differ by iron type:

• Ferrous iron is typically addressed with an oxidising filter — a manganese greensand or birm filter that oxidises the iron and then traps it. Aeration followed by filtration also works.
• Ferric iron needs sediment prefiltration before a finer polishing filter.
• Iron bacteria require chlorine dosing or UV disinfection, not just a mechanical filter.

The correct sequence and sizing depend on your iron concentration, your flow rate and whether other contaminants are present. A test result in milligrams per litre (mg/L) is what a reputable installer needs before specifying equipment.

Hardness: scale, soap scum and shortened appliance life

Hard water contains elevated levels of dissolved calcium and magnesium. It is extremely common in Joburg boreholes and causes a specific set of frustrations: white or grey scale deposits on geysers, kettles and showerheads; soap that does not lather properly; and a gradual reduction in geyser efficiency as scale builds up on the heating element.

Hardness is measured in milligrams per litre as calcium carbonate (mg/L as CaCO₃). SANS 241 sets an upper limit for aesthetic acceptability; water above that threshold is not dangerous to drink, but it is genuinely damaging to appliances over time.

The two main treatment options are:

• Ion exchange water softeners, which replace calcium and magnesium ions with sodium ions. These are effective but add a small amount of sodium to the water, which is a consideration for people on low-sodium diets.
• Template-assisted crystallisation (TAC) or electromagnetic conditioners, which do not remove hardness minerals but alter their crystal structure so they are less likely to form scale. Less maintenance, no salt, but effectiveness depends on water chemistry and application.

For a detailed breakdown of how these systems perform on borehole water specifically, the article on water softeners for hard borehole water is worth reading before you commit to a product.

If you're trying to work out which treatment suits your borehole water, getting installer input early saves money. Compare 3 free quotes — vetted installers, no obligation.

Smell: hydrogen sulphide and other odour causes

A rotten-egg or sulphur smell is the most alarming of the three problems — and also the one people most often misdiagnose. The usual cause is hydrogen sulphide (H₂S) gas, which forms when naturally occurring sulphate-reducing bacteria break down sulphur compounds in low-oxygen groundwater. The smell can be strong enough to make the water unpleasant to use even when iron and hardness levels are perfectly acceptable.

Less commonly, a musty or earthy smell comes from organic compounds — often from surface infiltration into a poorly sealed borehole casing, or from iron bacteria activity in the pump and pipework.

Treatment options for hydrogen sulphide include:

• Aeration — introducing air before filtration drives off the gas. Simple and effective for moderate concentrations.
• Activated carbon filtration — adsorbs hydrogen sulphide and many organic odour compounds. Works well at lower concentrations and is a common second stage after aeration.
• Chlorine dosing followed by filtration — addresses both H₂S and any associated bacteria simultaneously.

For earthy or musty smells linked to biological activity, disinfection of the borehole casing, pump and storage tank is often necessary alongside filter changes.

Why you should test before you treat

The temptation is to buy a combined filter system that claims to handle iron, hardness and odour all at once. Some do perform reasonably across all three. But the sizing, media and sequence matter: a system specified for moderate hardness will not cope with very high iron, and a carbon filter positioned before an iron filter will become fouled and ineffective quickly.

A proper water test — submitted to an accredited laboratory and compared against SANS 241 limits — costs relatively little and tells you exactly what concentrations you are dealing with. That result is the document you hand to an installer when asking for a treatment quote. Without it, you are buying on assumption.

It is also worth testing periodically after installation. Aquifer chemistry can shift seasonally, particularly after heavy rainfall events that change the recharge dynamics of the system.

What treatment systems typically cost

Treatment costs vary significantly based on water quality, flow rate requirements and the number of stages involved. As a rough guide only — confirm everything via installer quotes:

Treatment type	Typical installed cost range
Single-stage iron filter	R8,000 – R20,000
Water softener (ion exchange)	R12,000 – R30,000
Aeration + carbon filter combo	R10,000 – R25,000
Multi-stage whole-house system	R25,000 – R60,000+

These ranges are indicative. A high-iron borehole with bacterial contamination and very hard water may require a multi-stage system toward or beyond the upper end. A borehole with only mild hardness and a slight odour might be addressed at the lower end. Get itemised quotes from at least two or three installers who have seen your test results.

Once you have a water test result in hand, it's straightforward to get meaningful quotes. Get installer quotes here — free, vetted, no pressure.

Getting the sequence right matters as much as getting the products right

Even correct treatment products fail if they are installed in the wrong order. The general rule is: sediment prefiltration first, oxidation or aeration next if iron or H₂S is present, then softening if hardness is the primary issue, then carbon polishing for taste and residual odour, and UV disinfection last if biological safety is a concern.

Skipping stages or reversing them shortens media life, reduces effectiveness and can make problems worse. A reputable installer will explain the sequence they are proposing and why. If they cannot, or if they quote without asking for your water test results, that is a signal to get a second opinion.