What hard water is
Water picks up minerals as it passes through rock and soil, especially calcium and magnesium. The more of these dissolved minerals it contains, the “harder” it is described. Hardness varies widely by region and by the source of the supply, so two neighbouring areas can have quite different water. Your water supplier can usually tell you how hard the water is in your postcode, and many publish this on their website.
Hard water is generally not considered a health problem for drinking. Its effects are mostly practical: it affects soap, appliances and surfaces. Soft water, by contrast, contains little calcium and magnesium.
Why limescale forms
When hard water is heated, some of the dissolved calcium compounds come out of solution and form a hard, chalky layer, known as limescale. Evaporation does something similar on taps and shower screens, leaving white marks as droplets dry.
Limescale tends to collect wherever water is heated or sits and evaporates:
- kettle elements and the base of the kettle
- shower heads, where it can block the small nozzles
- taps and tile surfaces
- the heating elements and pipes inside washing machines and dishwashers
- boilers and hot water cylinders
How it affects appliances
A layer of scale on a heating element acts as insulation, so the element has to work harder to heat the water. In general, this can mean slower heating and somewhat more energy used, and over time scale can shorten the life of some parts. The size of these effects depends on how hard the water is, how often the appliance is used and its design, so it is best to avoid confident claims about exact savings or lifespans.
In washing machines and dishwashers, scale can also build up on parts that are not easy to see. White residue on dishes or stiff-feeling laundry is often a sign of hard water, though it can have other causes such as too much detergent or too little rinse aid.
Managing scale at home
Descaling
Regular descaling is the simplest approach. Kettles can be descaled with a descaler made for the purpose or with a mild acid such as citric acid dissolved in water, following the manufacturer’s instructions for the kettle. Rinse well and boil and discard fresh water before using the kettle again. Check your appliance manual first, because some manufacturers recommend particular products and others advise against certain acids.
Safety points:
- Never mix descalers with bleach or other cleaning products, because some combinations release harmful gases. If you want to know why, the basics are in the advice on mixing cleaners.
- Check the label for hazard symbols and follow the instructions.
- Keep descalers out of reach of children and pets, and ventilate the room.
- Do not use strong acids on surfaces such as natural stone, which can be etched.
Vinegar is often suggested as a cheap alternative. It can dissolve scale, but it has a strong smell, it may not be suitable for every appliance, and it can damage some seals and natural stone. Understanding what vinegar, bicarbonate and soap actually do helps you choose the right tool. Always check the appliance manufacturer’s advice.
Wiping and prevention
Wiping taps and shower screens dry after use stops droplets leaving marks. Soaking a clogged shower head in descaling solution, as the manufacturer allows, can restore flow. Not leaving water standing in the kettle also helps, and emptying it rather than reboiling old water is a reasonable habit.
Dishwasher salt, detergent and tablets
Many dishwashers have a built-in water softener that uses special salt to reduce hardness inside the machine. If you live in a hard water area, keeping this topped up per the manual can help. Do not put dishwasher salt into the detergent compartment. Some machines let you set the hardness level. Dishwasher use in a hard water area also tends to go better with rinse aid.
Water softeners and conditioners
For whole-house treatment, there are two broad types:
- Ion-exchange softeners swap calcium and magnesium for sodium or potassium, usually using salt. They genuinely reduce hardness, but they need salt refills, use some water during regeneration, need installation and cost money. Water from a softener may not be recommended for drinking by some guidance, particularly for people on sodium-restricted diets, so check the advice for your system.
- Scale inhibitors, magnetic or electronic conditioners are marketed as scale reducers without salt. Some inhibitors that change how scale forms have supporting evidence, while the evidence for magnetic and electronic devices is mixed, so be cautious about strong claims and ask for independent test data.
Whether a softener is worthwhile depends on how hard your water is, how many appliances you have and your budget. For many households, regular descaling and the right detergent are enough.
Environmental trade-offs
Descaling products, salt and softener systems all have a footprint, and wastewater from softeners adds salt to the sewer. On the other side, scale-free appliances can run efficiently and last longer, which spreads the manufacturing impact across more years of use. When choosing appliances, household appliances with a good record for repairability and service can help, and energy labels give a basic comparison. Using less hot water and keeping appliances in good working order make a difference in any water area.
This is general information. For boilers and hot water systems, ask a qualified engineer before you try to descale or treat the system.