The more dissolved calcium and magnesium water contains, the "harder" it is. Hard water is not usually a health concern, but when it is heated or evaporates it leaves a white deposit: limescale. Limescale clogs tap outlets, weakens shower heads, makes water heaters less efficient and leaves marks around the pool. You can find out how hard your water is from the local water authority, or measure it with simple test strips.
Taps and shower heads
The aerator on the tap outlet and the shower head are where limescale builds up first. If the flow has weakened and the water sprays sideways, limescale is usually the cause.
- Unscrew the aerator and, if possible, detach the shower head from the hose.
- Soak them for a while in vinegar or a citric acid solution.
- Clean with a soft brush, rinse well and refit.
On chrome or specially coated surfaces, leaving acid on for long can damage the finish. Check the manufacturer's cleaning advice.
Instantaneous heaters, hot-water tanks and combi boilers
Limescale builds up faster in any appliance that heats water. Scale on the heating element or heat exchanger makes it harder for heat to pass into the water. That means longer heating times and more energy use.
- Hot-water tank: The magnesium anode inside protects the tank from corrosion and wears away over time. Having the anode and element checked periodically extends the appliance's life.
- Instantaneous heater and combi boiler: Scale in the heat exchanger can be cleaned by a service engineer using a suitable method.
- Temperature setting: Keeping the water hotter than necessary can speed up scaling. Follow the manufacturer's advice, taking into account the temperatures recommended for hygiene.
Limescale in the pool
In a pool, limescale usually shows up as a white band along the waterline, deposits in the tile grout or cloudy water. Scaling depends on the hardness of the water and on the pH and alkalinity balance. If the pH is kept high, more scale is deposited.
- Test the pH and alkalinity regularly and keep them within the recommended range.
- Brush the waterline regularly; deposits are easier to remove before they thicken.
- If you have a heat pump or a salt chlorinator, follow the manufacturer's maintenance advice on scaling.
For balancing the pool water, see the order of chemical steps in the guide on opening your pool for the season.
Water softening options
- Ion-exchange softener: Fitted where the water enters the house, these systems reduce hardness significantly. They regenerate using salt, so the salt needs topping up and the unit needs regular maintenance.
- Sediment filter: Catches sand and rust but does not reduce hardness.
- Magnetic or electronic devices: Their effectiveness is disputed; look for independent information before buying one.
Which system suits you depends on the hardness of the water, how the house is used and how the plumbing is laid out.
Safety: Descalers contain acid. Wear gloves and eye protection and keep the area ventilated. Never mix a descaler with bleach or chlorine products, as toxic gas can form. Switch off the power before touching an electric water heater, and call an authorised service engineer for any internal parts.
Frequently asked questions
Is hard water safe to drink? Hardness is not usually a health issue, but whether water is drinkable depends on other factors too. If you're unsure, check the water authority's test results.
Does every house need a softener? No. If the problem is limited to a few taps and shower heads, regular cleaning may be enough. If the water heaters and plumbing keep giving trouble, softening can be worth considering.
Can limescale cause leaks? Limescale doesn't cause a leak on its own, but it can stop valves and seals from closing fully, which leads to dripping.
For limescale problems and plumbing maintenance, see the plumbing page.
This guide is for general information. Every home is different; for your own home, ask a company that has seen the work on site for a written quotation.