Hard water is not a health risk, but it is the most common water problem in UK homes. Around much of England, water picks up calcium and magnesium as it passes through chalk and limestone. When that water is heated or evaporates, the minerals come out as limescale: the white crust on kettles, taps and shower screens, and the hidden layer that coats boiler heat exchangers, immersion heaters and appliance elements.

At a glance

  • UK limit: none; hardness is not a health issue
  • Most affected: mains and borehole water from chalk and limestone areas
  • Signs: scale on kettles and taps, spotty glassware, stiff laundry, soap that won't lather
  • Fix: water softener, or scale reduction where softening isn't wanted
  • Check yours: enter your postcode in our free water hardness checker

What makes water hard?

Rain is naturally soft. As it soaks through chalk and limestone it dissolves calcium and magnesium carbonates, and the longer it spends in that rock the harder it gets. That is why the south and east of England tend to have hard water, while areas on granite, slate or peat, including much of Wales, Scotland and the north-west, are generally soft. Borehole water drawn from chalk or limestone aquifers is often very hard.

Hardness is usually measured in milligrams per litre as calcium carbonate (mg/l CaCO3), parts per million, or degrees Clark. Check your area with our free postcode water hardness checker, or test your own tap with our hardness test kit for an exact reading.

What hard water does to your home

  • Boilers and hot water cylinders. Scale forms fastest on the hottest surfaces. It insulates heating elements and heat exchangers, so they take longer to heat water and work harder to do it.
  • Appliances. Kettles, coffee machines, washing machines and dishwashers scale up and fail sooner.
  • Bathrooms and kitchens. White marks on taps, tiles and glass, and blocked shower heads.
  • Laundry and skin. Hardness minerals react with soap and detergent, so you need more of them, towels feel stiff and many people find their skin feels dry.

Is hard water safe to drink?

Yes. There is no legal limit for hardness in UK drinking water, and calcium and magnesium are not a health risk. Hard water is simply a nuisance and an expense.

If you soften your water, keep one unsoftened tap, usually in the kitchen, for drinking. Softened water contains more sodium, and the NHS advises against using artificially softened water to make up baby formula. A drinking water tap with a filter is a popular way to do this.

How to deal with hard water

Option How it works Best for
Water softener Ion exchange resin swaps calcium and magnesium for sodium, regenerated with salt. Removes hardness rather than just changing it. Whole-house protection and the most noticeable difference in bathrooms, laundry and skin. Browse meter-controlled, non-electric and eco models
Salt-free conditioning Treats water so hardness minerals are less likely to stick as scale, without removing them. Homes that want no salt or drain connection
Polyphosphate dosing Releases a small amount of polyphosphate that keeps minerals in solution and slows scale on heating surfaces. Protecting a single appliance, combi boiler or water heater
Electronic scale conditioners Clamp-on units that aim to change how scale forms; results vary with water and system. Where plumbing in a softener is not practical

Not sure which to choose? Our guide to water softeners for your home walks through sizing and options, and our commercial softener guide covers businesses.

Looking after a water softener

  • Keep the salt topped up with tablet salt; see softener salt.
  • Check the softened water every few months with a test kit.
  • Resin lasts many years, but iron or chlorine can wear it out sooner; replacement softener resin and parts keep older units running.

Hard water on a private supply

Very hard borehole water also coats the quartz sleeve of a UV unit, stopping it from disinfecting reliably. On private supplies, softening goes before UV disinfection. See borehole water and how to purify well water.

Related pages

Why Wrekin Water

Wrekin Water is a family run company based in Bettisfield, Shropshire. We have served more than 50,000 customers over 15 years, are rated Excellent on Trustpilot, and stock Pentair Fleck, Autotrol, Clack, Kinetico and other major brands. In North Shropshire we can install your softener. Ask our team which suits your home.

Frequently asked questions

No. Hard water is safe to drink and there is no legal limit for hardness in UK drinking water. It is a nuisance because it causes limescale in kettles, boilers and appliances and makes soap less effective.

Limescale forms when water containing dissolved calcium and magnesium is heated or evaporates. The minerals come out of solution and stick to surfaces, especially hot ones such as kettle elements and boiler heat exchangers.

A water softener removes the calcium and magnesium that form limescale, so new scale stops forming. Over time, softened water can also gradually reduce existing light scale.

Softened water is generally considered safe, but it contains more sodium, and the NHS advises against using artificially softened water to make up baby formula. Most installations keep one unsoftened drinking water tap.

A water softener removes hardness minerals using ion exchange and salt. Scale conditioners, polyphosphate dosing and salt-free systems leave the minerals in the water but aim to reduce how much scale they form. Softeners give the most complete result.