Understanding Arsenic in Drinking Water: A Guide for UK Homeowners

Sep 10, 2025

3 min read

Updated: Sep 21, 2025

Last reviewed: September 2026

Quick answer The UK standard for arsenic in drinking water is 10 micrograms per litre (10 µg/l, the same as 0.01 mg/l or 10 ppb), the same as the World Health Organization’s guideline value. Mains water is tested against it. The main risk is a private supply (a borehole, well or spring) in an area where the rocks contain arsenic, and the only way to know your level is to test.

On a private supply? The Arsenic Risk Check looks at your source, area and depth in under a minute.

Do the Arsenic Risk Check

The UK standard for arsenic

What	Level	Source
UK standard at the tap	10 µg/l	DWI drinking water standards
WHO guideline value	10 µg/l	DWQR
In other units	10 µg/l = 0.01 mg/l = 10 ppb	Conversion

“The WHO has set 10ug/l as the health based guideline value.” (DWQR)

For mains water, the DWI says: “All public water supplies are regularly tested in England and Wales and the results which are published and available to every consumer on request show that tap water is safe to drink” (DWI).

What arsenic is and where it comes from

The Scottish regulator describes arsenic as “a metalloid element that is found from time to time in water sources in the UK.” (DWQR)

Natural geology. “Arsenic is primarily a risk where it is naturally occurring in local mineral deposits.” (DWQR) “These can be quite localised” (DWQR).
Depth and pH. “In groundwaters, the concentration of arsenic can vary greatly with depth.” (DWQR) “There has been shown to be an association between higher pH groundwaters and higher arsenic concentrations.” (DWQR)
Man-made sources. “Man-made sources of arsenic include pesticides and timber preservatives.” (DWQR)

In Scotland, stream sediment studies found that “significant quantities of arsenic were found in sediments in Kintyre, Islay, Arran, Galloway and more generally in the Southern Uplands, and in parts of mid-North Perthshire around Crieff.” (DWQR) The regulator adds: “It can be inferred that private water supplies in these areas may contain elevated arsenic concentrations.” (DWQR)

Elsewhere in the UK, “studies by the British Geological Survey (BGS) into metal concentrations in stream sediments may be helpful in determining the risk from arsenic in a particular area.” (DWQR)

Why it matters

“Prolonged exposure to arsenic can cause skin lesions, skin, bladder and lung cancers.” (DWQR) The only way to know your level is a test.

Who should test

Private supply owners, especially boreholes, wells and springs in the areas above. In England and Wales a single home’s supply may never have been checked: “The regulations in England and Wales do not require mandatory monitoring to be undertaken at these supplies unless the local authority is requested to do so by the owner or occupier of the dwelling.” (DWI)
Anyone with more than one source. Test each one, after any treatment, at the tap you drink from.
Mains users. Mains water is already tested (see above), so a single home test is for peace of mind.

For a full testing plan for a private supply, use the Private Supply Planner.

If a test comes back high

Confirm it. “If a water sample fails for arsenic it would be prudent to gather additional samples to verify the failure and determine the variability of the concentration of arsenic in water.” (DWQR) Your council’s environmental health team can arrange a lab test.
Get advice. “Health advice should be sought.” (DWQR) Use another source for drinking and cooking while you wait for confirmation.
Treatment. “Point of use arsenic removal systems are available.” (DWQR) “RO membranes are well established as point of use treatment on private water supplies.” (DWQR) “Arsenic has a strong chemical affinity to iron, and a number of iron based adsorbents have been developed to exploit this.” (DWQR) Before you buy: “Professional technical advice should be sought” (DWQR).
Another source. “With naturally occurring arsenic it may similarly be possible to favour sources which have lower concentrations.” (DWQR)

Frequently asked questions

What is the safe level of arsenic in UK drinking water?

The legal standard is 10 µg/l, which matches the WHO’s health-based guideline value. See the DWI drinking water standards.

Is there arsenic in UK tap water?

Mains water is regularly tested against the standard. The main risk is a private supply in an area with arsenic-bearing rocks.

Can you remove arsenic from water?

Yes. Reverse osmosis at the tap and iron-based adsorbents are both used (see “If a test comes back high” above). Take professional advice on the right system for your supply.

How do I test for arsenic at home?

Screen the water you drink with an Arsenic Test, after any treatment. With more than one source, test each. A home screen is a first check, not a lab result.