3.4.2 Radiological aspects
Environmental radiation comes from a range of naturally occurring and anthropogenic sources, with the former estimated to contribute more than 98% of the radiation dose experienced by people (excluding medical exposure). Any exposure to radiation can lead to cancer, and the greater the exposure, the greater the risk.
The contribution that drinking water makes to radiation intake is very small, and is due largely to naturally occurring radionuclides (isotopes of an element which are unstable and undergo natural radioactive decay) in the uranium and thorium decay series.
Radon, a natural radioactive gas that has no taste, smell or colour, is estimated to contribute some 32% (of the above 98%) of the radiation people are exposed to. It is formed in the ground by the decay of uranium, which is often found in granite (and in phosphate-bearing rocks). Radon dissolved in water is released during handling of the water. Water that has been left to stand will have reduced radon activity, and boiling will remove radon completely. It is thus not seen as a problem.
There are strict guidelines on emissions of radioactive compounds, and the nuclear industry is carefully monitored. Nevertheless, to ensure water quality as regards radiation, limits are imposed.
The maximum dose from one year's consumption of drinking water has been set at 0.1 mSv. This is less than 5% of the average dose attributable annually to natural background radiation. For practical purposes, the maximum recommended guideline activity concentration is 100 Becquerel per litre (Bq l−1) for tritium (a substance coming largely from the nuclear industry). This is based on the consumption of 2 litres of water a day.