Water hardness

N21 London

Harder than the UK average. Expect visible limescale on kettles and taps.

At 307 ppm, London sits among the UK's hardest water areas — compare it against the softest areas.

Very Hard 307 ppm London Thames Water
Your reading
307
parts per million
Soft
Moderate
Hard
Very hard
0100200300400+

What this means for your home

Based on 307 ppm in London (very hard water).

  • Heavy limescale requiring frequent descaling
  • Blocked showerheads and reduced water flow
  • Substantially higher energy bills from boiler scale
  • Dry, itchy skin and lifeless hair
  • White crusty deposits on taps and surfaces
  • Reduced lifespan of washing machines and dishwashers
Heat loss
12%
Heavy scaling
Softener salt
£18–30
per year
Worth it?
Yes
at 307 ppm
Suggested for very hard water
Whole-house water softener
Best long-term protection for boilers and pipes.
From £600 installed
Shower head filter
A simple first step for limescale on tiles and glass.
From £25
Filter jug or under-sink
Improves taste and reduces kettle scale.
From £20
Softening

Should you soften the water in London?

A verdict and running-cost estimate based on N21's 307 ppm reading, for a typical 4-person household.

Softener recommended

Water is hard to very hard, so appliance, scale and soap savings typically pay back a softener within a few years.

Recommended size
24k
grain capacity, regenerates ~every 8.7 days
Salt running cost
£18–30
per year (~63 kg salt)
Limescale
12%
est. heater efficiency loss. Heavy scaling
Soap saving
High
Large saving: many homes cut soap, shampoo and detergent use by up to half.

Appliance impact at 307 ppm: significant: elements fur up, expect earlier failures. Sized for a 4-person home; regenerates roughly every 9 days (estimate). Figures are conservative estimates and vary with household size and usage.

Water quality details

Hardness data for N21

Sourced from Thames Water's published water-quality reports and public records.

Hardness measurements

Parts per million (ppm CaCO₃)307
Degrees Clark (°Clark)21.5
Degrees French (°fH)30.7
Degrees German (°dH)17.2
Calcium (mg/L Ca²⁺)123

Supplier and area

Water supplier Thames Water
Region London
County Greater London
Hardness band Very Hard
UK average 207 ppm
Visit Thames Water page
Official source
Thames Water Utilities Ltd water-hardness report

Read the hardness categories table to see where your supply falls; most of the region is hard to very hard at over 200 mg/l CaCO3.

Nearby

Other areas near London

N20
London
306ppm
Very Hard
N22
London
308ppm
Very Hard
FAQ

Common questions about N21

What is the water hardness in N21 London?
The water in N21 London has a hardness level of 307 ppm (parts per million) calcium carbonate, classified as very hard. This is 100 ppm above the UK national average of 207 ppm.
Which water company supplies N21?
N21 London is supplied by Thames Water. Thames Water serves the London region.
Is the water in N21 safe to drink?
Yes. Very Hard water at 307 ppm is safe to drink. Water hardness affects taste and can cause limescale, but it is not a health risk. In fact, hard water contains beneficial minerals like calcium and magnesium.
How can I reduce water hardness in N21?
For very hard water at 307 ppm, a whole-house water softener is the most effective solution. You can also use a jug filter for drinking water, descaling products for appliances, and a shower filter for better skin and hair.
What does 307 ppm water hardness mean?
307 ppm means there are 307 parts per million of calcium carbonate dissolved in the water. This is equivalent to 21.5 Clark degrees, 17.2 German degrees, or 30.7 French degrees. Water above 180 ppm is generally considered hard.
What size water softener do I need in N21?
For a typical 4-person home at 307 ppm, a 24,000 grain softener is a sensible size. It would regenerate roughly every 8.7 days. Larger households or higher daily use need a bigger unit. These figures are conservative estimates.
How much does it cost to run a water softener in N21?
At 307 ppm, expect to use about 63 kg of salt a year, costing roughly £18–£30/year. Water is hard to very hard, so appliance, scale and soap savings typically pay back a softener within a few years.

Check another postcode

Compare hardness across areas before moving or buying a softener.