Radon and radioactivity
Naturally occurring radioactivity in groundwater, mainly from uranium-bearing geology. For radon, the significant exposure is inhaling it after it comes out of the water, not drinking it.
Key facts
- Contaminant group
- Radiological
- World Health Organization — guideline
- 0.5 Bq/l gross alpha; 1 Bq/l gross beta as screening values
- European Union — legal limit
- 100 Bq/l for radon; 0.1 mSv/year indicative dose
- United Kingdom — legal limit
- 100 Bq/l for radon
- United States — legal limit
- 30 µg/l for uranium; 15 pCi/l gross alpha
Where it comes from
- Uranium and thorium decay series in granite, some sandstones and shales
- Radon dissolving into groundwater in contact with such rock
- Rarely, industrial or mining activity concentrating naturally occurring radioactive material
How it behaves in water
Radon is a gas and readily degasses from water into indoor air during showering, laundry and washing. Radium and uranium remain dissolved. Surface water is generally low in radon because it has already degassed; groundwater from granite terrains can be high.
How it is measured
Becquerels per litre for gross alpha and beta activity and for radon specifically. Screening is normally by gross alpha and beta, with speciation only if screening values are exceeded.
Regulatory position
| Jurisdiction | Value | Status | Notes |
|---|---|---|---|
| World Health Organization | 0.5 Bq/l gross alpha; 1 Bq/l gross beta as screening values | guideline | — |
| European Union | 100 Bq/l for radon; 0.1 mSv/year indicative dose | legal limit | — |
| United Kingdom | 100 Bq/l for radon | legal limit | — |
| United States | 30 µg/l for uranium; 15 pCi/l gross alpha | legal limit | — |
Table sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- European Commission — Drinking Water Directive (EU) 2020/2184 and reporting. Open — attribution required · European Commission reuse policy (Decision 2011/833/EU)
- Drinking Water Inspectorate — Drinking water quality in England and Wales. Open — attribution required · Open Government Licence v3.0
- United States Environmental Protection Agency — Safe Drinking Water Information System. Open · US Government work — public domain
Health context
Radon is an established lung carcinogen by inhalation, and the dominant risk from radon in water is the fraction that transfers to indoor air. Ingested radon contributes a much smaller dose. Uranium in water is a chemical kidney toxin at concentrations below those of radiological concern.
What removes it
| Row | Effective | Not reliably effective |
|---|---|---|
| 1 | Aeration, which strips radon effectively and is the standard treatment | Boiling in an unventilated space, which releases radon into the room |
| 2 | Granular activated carbon for radon in small supplies | Sediment filtration |
| 3 | Ion exchange or reverse osmosis for uranium and radium | Water softening for radon |
| 4 | Improving ventilation, which addresses the actual exposure route | — |
Occurrence
Concentrated in granite regions — parts of Cornwall, Devon, Aberdeenshire, Brittany and the New England states. Private supplies in these areas are the ones worth testing.
Related intelligence
Sources
- World Health Organization — Guidelines for Drinking-water Quality. Public but restricted · CC BY-NC-SA 3.0 IGO
- Peer-reviewed scientific literature — Open-access hydrology, water chemistry and water use research. Public but restricted · Publisher terms — public access, reuse not clearly granted