Hard water areas in London

Short version: if you're in London, your water's hard. Almost everywhere in the capital and the South East gets hard or very hard water, typically 250–300+ mg/l as calcium carbonate. Some streets come in a bit lower, some higher, but you'd struggle to find properly soft water anywhere inside the M25. Here's why, what the numbers mean, and how to check yours.

Why London's water is so hard

It's down to geology. A lot of London's water comes from the River Thames and the River Lee, and from groundwater pumped up from underground. On its way there, much of that water has soaked through chalk and limestone. Rain is naturally a little acidic, so as it trickles through the rock it dissolves calcium and magnesium and carries them along. That's what makes water "hard".

None of that's a health problem. Hard water's perfectly safe to drink. It's the limescale that's the nuisance: in kettles, on taps, on shower screens and inside boilers and hot water cylinders. Our post on hard water and your boiler explains what's going on behind the scenes.

What the hardness numbers mean

Hardness is usually given in mg/l (milligrams per litre) as calcium carbonate. These are the bands we use on our site:

• Soft: 0–50 mg/l
• Moderately soft: 51–100 mg/l
• Slightly hard: 101–150 mg/l
• Moderately hard: 151–200 mg/l
• Hard: 201–300 mg/l
• Very hard: over 300 mg/l

You'll sometimes see other units, especially on softener settings and test kits:

• Clark degrees (°Clark): divide mg/l by 14.3. So 300 mg/l is about 21 °Clark.
• German degrees (°dH): divide mg/l by 17.8. So 300 mg/l is about 17 °dH.

Most of London sits in the hard or very hard bands.

West and East London areas we work in

We're based in Chiswick and fit and service softeners across the whole of London. Most of our work is in these areas, all of which get hard or very hard water.

West London

• Chiswick (W4)
• Kensington (W8)
• Holland Park and Notting Hill (W11)
• Hammersmith (W6)
• Ealing (W5)

East London

• Shoreditch (EC2A)
• Hackney (E8)
• Bethnal Green (E2)
• Stratford (E15)
• Canary Wharf (E14)
• Walthamstow (E17)

The exact figure can vary between neighbouring streets and over the year, depending on which treatment works and sources are feeding your area at the time. So treat any single number as a guide, not gospel.

The Home Counties

It's much the same story outside London. We also cover Surrey, Kent, Essex, Hertfordshire, Buckinghamshire and Berkshire, where a lot of the water also comes from chalk and limestone and tends to be hard or very hard. If you've just moved here from somewhere with soft water, it can be a bit of a shock. Our guide to moving to London from a soft-water area has some tips for settling in.

How to check your water hardness

There are a few easy ways:

• Use our checker. Pop your postcode into the checker at the top of this page. The figures are an approximate guide to what's typical for your area, not official supplier data, but they're plenty to tell you whether a softener's worth thinking about.
• Check your supplier's website. Thames Water, Affinity Water, SES Water, South East Water and Essex & Suffolk Water all publish hardness by postcode.
• Get it tested. We test your water for free as part of every installation survey, so we can set any softener up for your actual supply.

There's more detail on all of this in our post: is my area hard water?

What you can do about it

You've got two real options. You can live with it: descale the kettle, wipe down the taps and keep an eye on the boiler. Or you can fit a whole-house water softener, which takes the hardness out where the mains comes in, so limescale stops building up all through the house. We always fit a separate unsoftened drinking tap in the kitchen alongside it. Find out how it works on our water softener installation page.

Frequently asked questions