Arsenic in drinking water: who is at risk, and how to check

What arsenic is, and why it matters

Arsenic is rare in UK tap water, but it matters where it occurs. Scotland's regulator describes it as “a metalloid element that is found from time to time in water sources in the UK.” DWQR

“Arsenic is both acutely and chronically toxic to humans.”

The main concern is drinking it over time: “Prolonged exposure to arsenic can cause skin lesions, skin, bladder and lung cancers.” DWQR “The WHO has set 10ug/l as the health based guideline value.” DWQR The legal standard at the tap in England and Wales is also 10 micrograms per litre DWI.

Where arsenic comes from

Arsenic comes mostly from the ground, and it varies a lot from place to place and even with depth. Tap a number on the diagram at the top of the page, or read the four points below.

Water chemistry plays a part too: “There has been shown to be an association between higher pH groundwaters and higher arsenic concentrations.” DWQR

Mains water or a private supply

Mains water is treated and tested. 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. Where arsenic occurs in a public source, it is treated: one method “has been used to remove arsenic on a number of public water supplies in the English midlands.” DWQR

Private supplies are where the risk sits. Groundwater from a borehole, well or spring may carry arsenic from the rocks, and a single home's supply isn't tested unless you ask. The DWI says “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

Areas with known arsenic

In Scotland, studies of stream sediments point to particular areas. The DWQR says “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 “It can be inferred that private water supplies in these areas may contain elevated arsenic concentrations.” DWQR

In England and Wales, the DWQR cites a survey of 1,200 groundwater sources: 6% were above the 10 µg/l guideline value, 1% were above 50 µg/l, and most (68%) were below 1 µg/l DWQR. So most groundwater is fine, but a small share isn't, and you can't tell which without a test.

For your own area, the DWQR notes that “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

If a test shows arsenic

1. 1. 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
2. 2. Use another source for drinking. We suggest bottled water or mains water for drinking and cooking until you know more, as a precaution while you confirm.
3. 3. Get advice. Tell your council, which can arrange a lab test. Any failure of the standard also exceeds the WHO value: “Health advice should be sought.” DWQR

The DWQR's checklist for finding the cause includes DWQR:

• “Is it likely that arsenic is naturally occurring, based on other sample data from supplies in the area and BGS data?”
• “Is there any history of industrial processes that could have used arsenic (paints, pesticides, timber preservation), or large accumulations of products that could have been treated with these products?”
• “If multiple sources, are concentrations of arsenic consistent across these?”

Treatment options

Sometimes the answer is at the source: “With naturally occurring arsenic it may similarly be possible to favour sources which have lower concentrations.” DWQR Otherwise, treatment. We don't sell treatment systems, so this is the DWQR's overview, not a recommendation.

Arsenic chemistry is complicated, so “Professional technical advice should be sought” DWQR before you choose. After fitting anything, retest the water you drink.