UK Hard Water Areas & Which Filter to Choose

Water hardness varies enormously across the United Kingdom. If you live in London or the South East, your water is likely very hard; head to Scotland or Cornwall and it is soft. The difference comes from the geology your supply passes through — chalk and limestone rock dissolve calcium and magnesium into the water, which is what we measure as hardness.

Hard water is not dangerous to drink, but it causes limescale build-up in kettles, on taps and shower screens, and inside pipes and appliances. It can also give water a flat, mineral taste that many people dislike. The right under-sink filter depends on how hard your water is and what you want to improve.

How hard is water in your region?

The map below summarises typical water hardness by region. For a precise figure, enter your postcode on your water supplier's website — they publish hardness levels for every supply zone.

Which filter should you choose?

Very hard water (London, South East, East Anglia): A dedicated limescale filter is your best starting point. These reduce the minerals that cause scale before they reach your kettle and appliances. Pair one with a carbon block filter to also remove chlorine and improve taste. See our limescale & hard water filters.

Moderately hard water (Midlands): A carbon block under-sink filter will handle chlorine taste and odour effectively. If you also notice scale on your kettle, add a limescale cartridge. Browse our under sink water filters.

Soft water (Scotland, Wales, South West): Limescale is not your problem, so a scale filter is unnecessary. A simple carbon filter improves taste and removes chlorine. If your home has old lead pipes, a reverse osmosis system will also reduce dissolved lead.

How to check your exact water hardness

The figures above are a guide. To find the precise hardness for your home, visit your water supplier's website and enter your postcode. Suppliers report hardness in milligrams per litre (mg/l) of calcium carbonate, or sometimes in degrees Clarke (°Clark). As a rule of thumb: below 100 mg/l is soft, above 200 mg/l is hard, and above 300 mg/l is very hard.