Hard water and limescale: what a filter can and can't do

What is hard water?

Hard water is water carrying a lot of dissolved minerals, mainly calcium and magnesium, picked up as it moved through rock and soil. It is not a contaminant and it is not a safety problem — hard water is perfectly safe to drink.

The trouble is what those minerals do when water is heated or left to evaporate. They come out of solution and deposit themselves as limescale: the chalky white crust in your kettle, the film on your shower screen, the scale that builds up inside a geyser and quietly makes it work harder.

How do I know if I have hard water?

The everyday signs are reliable enough. White crust in the kettle. Spots on glasses after the dishwasher. Soap and shampoo that will not lather properly. Showerheads that block up.

For anything beyond a guess, you need a water test, and if you are on municipal supply your water authority publishes quality data that will include hardness. Borehole water is where hardness is most likely and most variable, which is a good reason to test before you buy any treatment.

Will a water filter soften my water?

No, and this is the part worth being straight about. Sediment and carbon cartridges do not remove dissolved minerals. A carbon filter is superb at chlorine, taste and odour, and it will do nothing measurable about hardness. Fitting one and expecting a scale-free kettle is a disappointment waiting to happen.

Softening hard water properly is a different category of equipment from anything in a standard filter housing, and if your test comes back with significant hardness that is a case for asking for advice rather than guessing at a cartridge.

One technology in the range does reduce dissolved minerals: a reverse osmosis membrane. But RO is a drinking-water solution at one tap, not a whole-house answer to limescale in your geyser — it is slow, it sends some water to drain, and it is not designed to treat everything entering your home.

But doesn't the calcite stage add minerals? Isn't that the opposite?

It is the opposite, and the distinction matters. The calcite cartridge in the 4-Stage Whole House system exists for water that has too few minerals, not too many — rainwater and soft, corrosive supplies that are slightly acidic and nibble at pipes. Calcite adds calcium back to take the edge off that acidity.

So the two problems pull in opposite directions. Soft, hungry water needs minerals added to protect your plumbing. Hard water already has more than it needs. Fitting a calcite stage to a hard-water home is solving a problem you do not have.

So what can help?

In the shower, the SUPERPURE Satin Chrome Shower Filter helps minimise limescale build-up alongside its main job of reducing chlorine, chloramines, heavy metals and sediment. That is a comfort improvement at one fixture, not a whole-house cure.

For everything else, the honest advice is unglamorous: descale the kettle and showerhead regularly, and have your geyser looked at on schedule if you are in a hard-water area. We would rather tell you that than sell you a cartridge that was never going to work.