How Isleworth compares
At 275 mg/L (19.3 °Clark), Isleworth is 13% above the median of the 411 English towns on this map (243 mg/L). It ranks 124 of 411 for hardness (1 is the hardest).
Water hardness in Isleworth
Isleworth has hard water: expect visible limescale and plan to descale regularly.
Data
| Value | 275 mg/L calcium carbonate 19.3 °Clark, 15.4 °dH |
|---|---|
| Band | hard |
| Area | Greater London |
| Population | 25,008 |
| Water company | Thames Water |
| Postcode checked | TW7 4HS (NLW59) |
| Checked | 21 Oct 2026 |
| From the source | “Hardness (Total) as CaCO3 (mg/l) min 263 mean 275 max 287 | "mapCode":"NLW59"” |
What it means for your home
Hard water drops a lot of scale when it is heated: in the kettle, the shower head and the element of an immersion heater or washing machine. Chalky rings on taps and spotty glasses are normal.
Set the dishwasher for hard water, dose detergent for your band and descale regularly. If you have a combi boiler, ask about a scale reducer at its next service. Hard water is safe to drink.
How often to descale
As a rule of thumb for hard water, kettles and shower heads need descaling every three or four weeks. Descale whenever you see scale building up.
Common questions
Is hard water bad for you?
No. Hard water carries calcium and magnesium, minerals the body uses. Whether tap water is safe depends on germs and pollutants, which water companies test for, not on hardness.
Do I need a water softener in Isleworth?
The water company's figure for Isleworth is 275 mg/L (19.3 °Clark), which is hard water. Usually not straight away. Set the dishwasher, dose detergent for your band and descale regularly. Get quotes for a softener only if scale is clearly damaging your boiler or appliances.
How do I find the value for my address?
Use your water company's postcode checker. Hardness can differ between districts, so check your own postcode, or test with strips or a drop test.
Nearby towns
Hounslow 1 km Heston 2 km Richmond 3 km Southall 4 km Hanworth 5 km Feltham 6 km Acton 6 km Greenford 6 km