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When hard water is heated, the dissolved calcium and magnesium bicarbonates break down to form less soluble calcium and magnesium carbonates. These precipitate out of the water to form solid limescale. Signs of limescale include:
Scale from hard water is usually white, but can become coloured by traces of other minerals or metals. For example, traces of copper from plumbing materials can turn it grey, green or blue while traces of rust from pipework can turn it orange, brown or black.
You can do a quick and safe test to confirm limescale particles by placing some of the particles in a glass and slowly adding a few drops of ordinary vinegar or a solution of half a teaspoon of citric acid (lemon juice) dissolved in half a cupful of water.
The limescale should fizz slightly, giving off bubbles of carbon dioxide gas. This confirms that the particles are naturally occurring hardness minerals. The liquid in the glass may change colour if metals such as copper are dissolved as well.
You are more likely to see scale in water boiled in plastic kettles than metallic ones because they are smoother and hold the scale less firmly. To reduce scale:
Some water filter jugs can partially soften water to reduce the formation of floating scum. If you choose to use a filter jug, please check that the replaceable cartridge is designed for softening and always follow the manufacturer's instructions.
Dishwashers usually have a built-in softener which uses salt to reduce the hardness of the water, preventing the formation of a white film on glassware or crockery and helping to prolong the life of the appliance itself. Make sure you replenish the appropriate dishwasher containers with salt and rinse aid when they need it.
Some dishwashers require setting to a water hardness level to get the best performance - refer to your appliance manual for instructions on how to set the hardness level.
You can find out the hardness of your water supply using our
Please note that the results are given in several different units so do ensure that you use the correct value as required in the instructions.
Limescale can build up in and around taps and shower heads fed from the hot water system.
These items can be cleaned from time to time using descaler or by carefully using vinegar or citric acid (lemon juice) solution and rinsing fully afterwards.
We do not soften water artificially during the treatment process and do not recommend softened water for drinking and cooking purposes. If you prefer your water to be soft, you may wish to install a domestic water softener in your home.
Some water softeners use an ion exchange system to replace the calcium and magnesium, the minerals that cause water hardness, with sodium. Others softeners use a reverse osmosis system to remove these minerals.
Water softeners can reduce scale in your hot water system, showers and on sanitary fittings and help to prevent the formation of scum when using soaps and detergents.
If you choose to have either variety of water softener fitted, it is recommended that you have a separate tap installed to supply unsoftened water straight from the mains for drinking and food preparation.
For ion exchange systems this is due to the higher concentration of sodium involved in the softening procedure. For this reason, softened water is not advised for use with powdered milk for baby feed as it already contains sufficient sodium and very young babies have a limited tolerance. Those on low sodium diets should also seek advice from their doctor.
Reverse osmosis treated water is not generally considered suitable for drinking and cooking as reverse osmosis not only removes hardness minerals, but changes the natural properties and even the taste of tap water.
These alter the nature of the hardness minerals which form hard scale when the water is heated. Unlike softeners, they do this without changing the chemical content of the water.
Water conditioners encourage dissolved hardness minerals to remain suspended in the water rather than attaching themselves on to the heated surfaces and pipework.
This means solid scale does not form when conditioned (treated) water is heated, and when it dries a soft scale may form which can be cleaned or wiped away easily.
There have been reports that in some circumstances conditioners do not work or are not as effective as expected.
It should also be pointed out that water conditioners do not soften the water, ie, lower the calcium level, which ultimately is the only way to combat the effects of limescale. This is why we don't recommend using water conditioners.