Which Borehole Water Filter Do You Actually Need?

Plenty of Paarl homes put in a borehole for the garden. Then the second thought arrives: if the water is free, why not run the house on it too? That is often when the problems show up. The basins go orange, the shower glass goes white, the geyser starts to rumble, and the search for a borehole water filter begins.

What you find is a shelf of boxed kits, each promising clean water. Some of them are useful. Most are the wrong tool for the job, because borehole water does not come with a standard set of problems. Two holes on the same Paarl street can draw quite different water, and the filter that fixes one may do nothing for the other.

So this guide works the other way round. It starts with what your water actually contains, matches each result to the stage that deals with it, puts those stages in the right order, and then covers how the whole system should be plumbed so it keeps working past the first month.

Start with the test, not the shop

Every decision below hangs off a water analysis from a SANAS-accredited laboratory, measured against SANS 241, the South African drinking water standard. Our guide to borehole water in Paarl explains what that test covers and what it costs. For choosing a filter, these are the results that decide the design:

• Turbidity, how cloudy the water is. SANS 241 sets an operational limit of 1 NTU.
• pH, the acceptable range is 5 to 9.7. Low pH means the water is attacking your pipes.
• Iron and manganese, which stain at very low levels. The aesthetic limits are 0.3 mg/l for iron and 0.1 mg/l for manganese.
• Hardness, the calcium and magnesium that scale geysers and taps.
• E. coli and coliforms. SANS 241 requires E. coli to be absent.
• Nitrate, with an acute health limit of 11 mg/l as nitrogen.
• Total dissolved solids, chloride and sodium, the salinity markers. The aesthetic limit for total dissolved solids is 1 200 mg/l.

That last group deserves attention in Paarl. Many boreholes here draw from the Malmesbury Group, the shale and metasedimentary rock under the valley around Paarl Mountain's granite. A 2019 study that included 30 boreholes near Paarl notes that this aquifer has been characterised by relatively higher salinities. Salt is the one problem most home filters cannot touch, so you want to know about it before you spend anything.

Match each result to the stage that fixes it

Here is what each problem needs, and the limits of each fix. If a result is within its limit, you do not need that stage, which is how a sensible system stays smaller and cheaper than the one in the brochure.

• Sand, grit and cloudiness: a sediment filter. A spin-down screen or a cartridge filter rated in microns. It is the first stage on almost every borehole, because it protects every stage after it.
• Acidic water: a neutraliser. The tell-tale sign is blue-green staining under taps, which is copper dissolving out of your pipes. A calcite neutraliser raises the pH of mildly acidic water, roughly pH 6 to 7, by dissolving into it. That means it adds a little hardness as it works. More acidic water usually needs a dosing system instead.
• Dissolved iron and manganese: an oxidising media filter. This is the stage people most often get wrong. The Minnesota Department of Health, which publishes some of the clearest guidance on private well water, rates oxidising media filtration as more effective than other oxidation and filtration methods for iron and manganese. It puts a manganese greensand filter at up to 10 to 15 mg/l of iron. Above about 10 mg/l, the water is often oxidised first, with air or chlorine, and then filtered. These filters clean themselves by backwashing, which matters for the plumbing later.
• Hardness: an ion-exchange softener. It swaps calcium and magnesium for sodium and regenerates with salt. It is not an iron filter. The same health department notes that while some manufacturers claim up to 10 mg/l, 2 to 5 mg/l of iron is a more common limit for a softener. Softening adds some sodium to the water and can affect how corrosive it is.
• Taste, odour and colour: activated carbon. Useful for a final polish. But a carbon filter that is not changed on schedule can grow bacteria and eventually release what it has trapped.
• Bacteria: UV disinfection. A UV lamp kills bacteria and viruses without adding chemicals. It leaves nothing in the water to protect it downstream, and it only works on clear water.
• Salts and nitrate: reverse osmosis. A membrane removes dissolved salts, sodium, chloride and nitrate, the things nothing else on this list touches. It also sends a large share of the water it receives to drain, and it needs pretreatment so iron and hardness do not clog the membrane.

The order the stages go in

Get the sequence wrong and good equipment fails quickly. For a whole-house borehole supply, the stages normally run like this:

1. Sediment filter. Sand first, so nothing downstream fills up with grit.
2. pH correction, if the water is acidic. Many iron filter media need water close to neutral to work.
3. Iron and manganese filter. The metals come out before they can foul a softener's resin or stain anything else.
4. Softener, if the water is hard.
5. Carbon filter, optional, for taste and odour.
6. UV disinfection, last. Closest to the taps, after everything that clouds the water or coats the lamp.

Reverse osmosis sits outside that line, under the kitchen sink, feeding a dedicated drinking water tap from water that has already been through the stages above.

Why the boxed kit disappoints

The typical boxed "whole-house" kit is two or three cartridge housings in a row: a sediment cartridge, then carbon. As a first stage that is perfectly useful. It takes out sand and improves taste. What it does not do is the job most people buy it for.

Dissolved iron is not a particle, so it passes straight through a sediment cartridge. It only becomes a particle once it meets air, which then happens inside your basin, your toilet cistern and your washing. Sometimes it happens partly inside the cartridge, which then clogs and goes orange. A cartridge kit also does nothing for hardness, nothing for salts, and nothing for bacteria.

That is how a lot of homeowners conclude that borehole filters do not work. Usually the filter worked exactly as designed. It was just the wrong stage for the water.

Whole house, kitchen tap or garden only?

Before choosing equipment, decide which water you are actually trying to fix. Treatment comes in two forms: point-of-entry, which treats all the water entering the house, and point-of-use, which treats water at one tap, usually for drinking and cooking.

• Garden and irrigation. Plants do not need treated water. A sediment screen to protect the sprinklers is usually enough. The exception is iron-rich water sprayed onto walls and paving, which leaves the same orange staining as in the basins.
• The whole house. If the staining and scale are inside the house, the treatment has to be point-of-entry. Remember the connection rule: under section 56(5) of the by-law, borehole water may never be connected to plumbing that is also on the municipal supply. A house running on borehole water needs its own supply, usually through a break tank with an air gap, and the treatment train goes on that line.
• Drinking water only. If the house runs happily on borehole water but you want to drink it, a point-of-use system at the kitchen tap, often reverse osmosis followed by UV, is far cheaper than treating every litre that goes into the toilets.

There is a fourth option many people overlook. Keep the house, and especially the geyser, on the municipal supply, and run the borehole to the garden, the pool and the toilets on separate lines. It needs the least treatment of all, and it avoids most of the damage hard or iron-rich water does indoors.

How a filter system should be plumbed

The equipment gets the attention, but the plumbing decides whether the system still works in a year. On a properly installed borehole system, look for these things:

• The right position. Treatment goes after the borehole pump and pressure tank, or after the booster pump on a break tank, and before the house supply.
• A bypass. Valves around the system, so it can be serviced without leaving the house dry.
• A proper drain. Backwashing filters and regenerating softeners both send water to drain, so the system needs a drain point connected to the sewer. Softener brine in particular should never be run onto the garden.
• Enough flow to backwash. A media filter cleans itself by pushing water back through its bed, and it needs a strong flow to do it. Paarl yields are decided by fractures in the rock, and Malmesbury Group holes that miss them have long been known for low yields. On a weak hole the backwash has to come from storage, and the design should follow the yield test, not the brochure.
• A sample tap after the last stage, so the treated water can be tested without dismantling anything.
• Marked pipework. Where a property has both municipal and borehole water, section 53(4) of the by-law requires the pipework to be colour-coded and signposted, so nobody connects the two by mistake.
• A protected geyser. If the water is hard and the geyser is on the borehole supply, the softener must sit upstream of it. Scale is what burns out geyser elements, and a geyser repair is a costly way to find out the softener was in the wrong place.

Keeping it working

Every treatment stage needs looking after, and an unmaintained one is worse than useless. The Minnesota health department warns that treatment units that are not maintained lose their effectiveness, and that in some cases they can make water quality worse. In practice:

• Test the treated water once the system is installed, and again periodically. Groundwater quality changes with the seasons and with what happens on the land around the hole.
• Change sediment cartridges when the pressure across them drops, and carbon cartridges on the manufacturer's schedule, whether or not they look dirty.
• Keep the softener supplied with salt, and check its regeneration settings if your household or water changes.
• Replace the UV lamp on schedule, typically once a year, and clean the quartz sleeve. A UV lamp can glow long after it has stopped disinfecting.
• Check the backwash on media filters, because a filter that cannot backwash properly slowly turns into a blockage.

None of this is complicated, but it is the part that turns a filter purchase into clean water for years. If you want a system matched to your test, sized to your hole and plumbed so it can be serviced, that is exactly what our borehole water filtration in Paarl covers, with the price agreed before we start.