London tap water: drinking quality, hardness and filters

Katerina Galkina · EN · 07/10/2026

Establish why you are concerned

Public mains drinking water is subject to quality controls. The Drinking Water Inspectorate explains that a routine domestic filter is unnecessary for health protection when the supplied water meets normal standards ↗. This does not override local incident warnings or a problem with a particular building’s plumbing.

If colour, smell or taste changes suddenly, check supplier notices and contact the water company. Compare the cold kitchen supply with other taps, note when the issue began and inform the landlord. Do not try to solve an unidentified supply fault by buying an advertised filter.

Separate hardness from safety

Hardness comes from dissolved calcium and magnesium ↗. It affects limescale and appliance maintenance. White deposits in a kettle do not, by themselves, demonstrate dangerous contamination.

Identify the supplier and request water quality and hardness information for your address. Do not assume that readings from another London property apply to yours. Follow the descaling instructions for your kettle or coffee machine separately: appliance maintenance is not a drinking-water test.

Choose a solution for a defined purpose

A carbon filter may help with an unwanted taste. Compare the purchase price and annual replacement cartridge cost, capacity, installation space and availability of consumables. Ask precisely what it removes and what testing supports those claims.

As a simple taste comparison, try refrigerating water in a clean, covered jug. Whole-home softening serves a different purpose: it replaces calcium and magnesium with sodium. DWI recommends retaining a separate unsoftened kitchen tap for drinking. In rented accommodation, obtain agreement before altering plumbing.

Maintain the filter and calculate the full cost

Replace cartridges according to the instructions and clean the container regularly. A neglected filter is not necessarily safe because the water looks clear. When comparing filtration with bottled-water delivery, include storage, lifting, delivery charges and equipment maintenance.

Do not commit to an expensive system after a salesperson’s demonstration “contamination test” without checking with the water company. If an official water warning applies, follow its specific instructions. A domestic filter is not a universal substitute for the prescribed precautions.