Blue water droplet splash forming a mushroom shape above a glass of clear water on a pale background

Can you drink tap water in London?

October 25, 2026

You moved to a London flat, the kettle furred up in a fortnight and a friend says only bottled water will do. What do the official figures say, and what do they leave out? You can check your own tap with a 20-in-1 test strip.

Short answer: The DWI reports that 99.97% of tests on England's public supplies met the legal standards in 2025, and Thames Water supplies most of London. That is an area figure. London water is hard to very hard, and the DWI says 37% of the 586 water quality events it was told of in 2025 were attributed to consumers' distribution systems.

By Andrew Tomlinson, WaterKit · Last reviewed 29 October 2026

How good is London's tap water, going by the official figures?

The headline figures are high. The Drinking Water Inspectorate (DWI), the regulator, says public supplies in England met the legal standards in 99.97% of tests in 2025, with 99.95% for chemical parameters and 99.98% for microbiological ones. They came from 24 water companies serving 59.74 million consumers. We found no separate London figure from the DWI.

Thames Water, which supplies most of London, says more than 99.95% of tests on samples from customers' taps have met the legal standard since 2010. That is the company's own figure, not the regulator's.

Who supplies tap water in London?

Four main companies, by our reading of the sources below, with Thames Water covering most of the capital. Water UK says Thames Water is responsible for the public water supply in most of Greater London. Some new-build estates are served by smaller new appointment companies, the DWI says.

Supplier	Where it supplies in London	What it says about hardness
Thames Water	Most of Greater London, per Water UK	All water in its region is hard. Battersea North averaged 258 mg/l and Kingston North 259 mg/l, from four samples each
Affinity Water	Harrow and Hillingdon, and parts of Barnet, Brent, Ealing and Enfield	Classes its water as hard or very hard. Our lookup for one Harrow postcode (HA1 1BD) returned 363 mg/l, which it calls very hard
SES Water	South London, from Morden and South Croydon southwards	Says many of its sources are naturally hard. Its checker classed our SM1, SM2 and SM4 postcodes as hard
Essex and Suffolk Water	Barking and Dagenham, Havering and Redbridge	Says water is probably hard where the source is near chalk or limestone, and that blended supplies vary. We found no London figure

Your postcode decides which one is yours. Your bill will say, or use the Find your supplier tool on the Water UK home page.

Does London have hard water?

Yes. Thames Water and Affinity Water class the water they supply as hard or very hard, and SES Water's checker classed each south London postcode we tried as hard. The DWI says hardness is dissolved calcium and magnesium, and classes it in mg/l of calcium carbonate like this.

DWI class	mg/l CaCO3
Soft	Up to 100
Slightly hard	100 to 150
Moderately hard	150 to 200
Hard	200 to 300
Very hard	More than 300

There is no UK standard for hardness, the DWI says. It lists scale in kettles and heating elements, less lather and tide marks on basins as the effects. Our guide to why London water is so hard covers the geology.

SES Water's checker gives hardness as mg/l of calcium, but its 2025 zone reports give it as calcium carbonate, at 205.2 mg/l for Langley Park Morden and 209.5 mg/l for Nork, the zones our postcodes fell in. That is the bottom of the DWI's hard band. For other postcodes, see our hardness by postcode guide.

Why might the water at your London tap differ from the area figure?

Because the area figure is an average. Your tap sits at the end of the last metres of pipe, any tank in the loft and the plumbing of a building of a certain age, and the DWI's 2025 report shows how much of its caseload sits there. It says 217 of the 586 water quality events it was notified of in England in 2025, or 37%, were attributed to consumers' distribution systems, and that 447 of the year's compliance failures related to consumer distribution systems.

“If your tap is at the end of old pipework or a loft tank, I would treat the area figure as a starting point and check your own water before assuming it matches.”

Andrew Tomlinson, WaterKit

The same report records events nearer London's mains. The DWI's events chapter says Thames Water's Ashford Common works, which supplies more than 4.2 million consumers in combination with other sources, recorded bromate of up to 56.9 µg/L in July 2025 against a 10 µg/L prescribed value, after an ozone dosing fault between 10 and 15 July. The DWI says concentrations stayed below short-term health-based guidance values and that the fault was resolved on 15 July. At Kempton Park works, which contributes to supplies serving around 4.25 million people across north and south London, single Cryptosporidium oocysts were found in three samples in February 2025, and the DWI says all later samples were clear.

The enforcement chapter lists 5 notices to Thames Water under regulation 28(4) in 2025, and 92 recommendations, the most of any company.

Do older London homes have lead pipes?

Some may. The DWI says a home built before 1970 may have lead pipes, and one built after is unlikely to. It says many older properties that have not been modernised are likely to have lead pipework underground, inside the building or both.

England-wide, 60 of more than 14,000 lead samples failed the 10 micrograms per litre standard in 2025, according to the DWI. Its report says lead is to a large extent confined within the boundaries of homes, and so under the owner's control.

Check. The DWI says to look at the pipe where water enters the home. Unpainted lead is dull grey, often with a swollen joint, and scraping it gently with a coin, wearing gloves, shows shiny silver metal. Our lead pipes guide goes through it.
Standing water. For drinking and cooking, the DWI says to run the tap to clear water that has stood in the pipes for a while, such as overnight.
Who owns what. The water company owns the communication pipe from the main to your boundary stop valve. The property owner is responsible for the rest. The DWI recommends a qualified plumber, such as one on the WaterSafe scheme, and says to tell your water company, which is legally required to replace its own pipe if it is lead and at risk of adding to the lead in the water.
Replacement scheme. Thames Water says it can replace its lead pipework when you replace yours, if you qualify. Its page said the scheme was due to close temporarily in November and reopen in spring 2027.

What about loft tanks, bathroom taps and flats?

The DWI's advice is to drink from the kitchen mains tap where you can. It says that ideally you should use a mains tap for drinking, food preparation or teeth cleaning, and that tank-fed water can be used if the tank is properly designed, correctly installed and kept in good condition. In older houses the kitchen cold tap may be the only mains tap. Our loft tank guide explains what the tank does.

To tell, the DWI suggests holding your thumb over a fully open tap. If you can hold the water back, the tap is likely tank-fed, and a plumber can check. It also says not to use hot water or bathroom taps for drinking or cooking, because that water usually comes from a loft tank. Our bathroom tap guide covers the details.

If you rent, the DWI says tanks in public buildings, workplaces, health care premises and social housing must be checked and cleaned for legionella control, and that a private landlord is responsible for those checks. A tenant can ask the landlord or managing agent whether the drinking water comes from storage.

How can I check my own tap in London?

Start with your supplier's postcode checker, though a zone report is not specific to any one property. Then test your own tap.

Fill a clean glass or cup, dip one 20-in-1 strip, wait 30 to 60 seconds and match the pads to the chart, or scan the QR code on the chart to enter the colours in our free results checker. Try the kitchen and a bathroom tap side by side. The optional bacteria test is read after 24 to 48 hours. A strip result is not a legal sample, and the strip cannot read lead at the UK limit, so for lead use the DWI's pipe check above.

Check	UK figure	What our chart can show
Hardness	No UK standard	Steps at 100, 250 and 425 mg/l. Read as calcium carbonate, the 250 step sits in the DWI's hard band and 425 in its very hard band
Copper	2 mg/l	Steps at 0.2, 0.5, 1, 2 and 5 mg/l, so it can show a reading under, at or over the standard
Free chlorine	No UK limit	Steps at 0.5, 1 and 3 mg/l. The DWI says companies typically keep it at 0.5 mg/l or less, and our portal calls up to 1 mg/l typical
Lead	0.01 mg/l	The first colour step is 20 mg/l, so the strip cannot read lead at the UK limit
Coliform bacteria	None in 100 ml	A yellow result indicates coliforms are present in that sample. It is a presence screen, not a count

The area figure is an average, and the DWI attributed 37% of the 586 water quality events in 2025 to consumers' distribution systems, so your own tap may differ. The hardness, copper and free chlorine pads matter most here. A kitchen and bathroom reading that differ would indicate the two taps are fed differently, and a copper reading above the lower steps would be worth raising with a plumber. Best pack: 20 strips, enough to compare two taps now and re-test after any plumbing work, £5.99 (or £10.99 with a bacteria test), with free 2nd Class delivery on every order. See the kit

Your London tap water questions

Is London tap water safe to drink?

The DWI reports that 99.97% of tests on England's public supplies met legal standards in 2025, and says that should give consumers confidence but must not lead to complacency.