Guide
Hard water and limescale in Cotswold homes
Short answer
Cotswold water is hard because it runs through limestone. Hard water is not harmful, and there is no legal standard for hardness. It does leave limescale in kettles, showers, cylinders and boilers. You can cut it with simple steps, a scale inhibitor or a water softener. Keep one unsoftened tap for drinking.
Why the water is hard
Water picks up minerals as it passes through rock such as chalk and limestone. The Cotswolds stand on limestone.
Thames Water says all the water in its region is hard. Thames Water supplies parts of the Cotswolds, such as Bourton-on-the-Water. Your water company can tell you the hardness at your postcode.
How hard water is measured
Thames Water uses these bands, in milligrams of calcium carbonate per litre.
| Band | Hardness (mg/l as calcium carbonate) |
|---|---|
| Soft | Up to 100 |
| Slightly hard | 100 to 150 |
| Moderately hard | 150 to 200 |
| Hard | 200 to 300 |
| Very hard | Over 300 |
Bands published by Thames Water on its hard water page, checked on 15 October 2026. Other water companies may use different bands. Sources: Thames Water: hard water.
Is hard water safe?
Yes. Thames Water says hard water is not harmful. The DWI says the drinking water rules set no standard for hardness.
The DWI quotes the World Health Organization: water at 200 mg/l or more causes scale. Soft water at 100 mg/l or less is more corrosive to pipes.
How to cut limescale
Start with the simple steps that Thames Water suggests.
- Set your hot water to 60°C.
- Put a steel scale collector in the kettle, and empty the kettle when you do not use it.
- Clean shower heads and taps often.
- Ask a plumber about a scale inhibitor on the boiler or cylinder.
- Think about a water softener. Keep one tap on unsoftened water for drinking and cooking.
Water softeners
A softener removes the minerals that make scale. It also adds sodium to the water.
Approved Document G says softened water should not replace wholesome water at a drinking tap or a kitchen sink. The DWI says softening only the water to the boiler or cylinder can cost less than softening the whole house.
A softener that uses water to regenerate needs notice to the water company before it is fitted. Our page on water softeners explains more.
Questions
Is hard water bad for my boiler?
Limescale can build up in boilers, cylinders and immersion heaters, and make them less efficient. Ask a plumber about scale protection when you fit a new boiler or cylinder.
Can I drink softened water?
Keep a separate tap with unsoftened water for drinking and cooking. Softeners add sodium, which can be a problem for premature babies and people on a low-sodium diet.
How do I find the hardness of my water?
Ask your water company, or use the water quality check on its website. Your bill names your water company.
Sources
- Thames Water: hard water
- Drinking Water Inspectorate: water hardness
- GOV.UK: Approved Document G, sanitation, hot water safety and water efficiency (2024 amendments)
- Thames Water: increased lead levels in Bourton-on-the-Water
- legislation.gov.uk: Water Supply (Water Fittings) Regulations 1999, regulation 5 (notice and consent)