1. Radon in water
Underground water always contains a certain radon amount, while the radon concentration in surface water is negligible. Radon enters into water from rocks that contain uranium and radium, and radon enters together with water into houses. Radon releases to the atmosphere if you use water in houses (during showering and washing about 50 percent, and during cooking and washing nearly 100 percent); and short-lived radon daughters are also generated. Their inhalation contributes to the exposure to the population. Nevertheless, from the standpoint of exposure, drinking water is less significant.
How to measure radon in water?
The measurement of the radon concentration in water is carried out in a laboratory. The samples of water with a volume of about few tenths of litre are taken into the special containers that are sealed to prevent radon release, and the measurement should be performed within four days after sampling. The measurement of the radon concentration in water is classified as the most significant performance from the standpoint of radiation protection, and hence, the measurements need SÚJB permission. About 20 companies have received this permission, and their list can be found on SÚJB web page www.sujb.cz
The mean value of the radon concentration in drinking water from underground water sources in the Czech Republic is about 14 - 15 Bq/l (according to the results in 2015), and the maximum values found have reached the order of about thousands of Bq/l, (for interest's sake, water used for treatment in Jáchymov Spa has a value of about 10,000 Bq/l). The radon concentration in water is linked with the content of natural radionuclides in geological subsoil (see the geological radon risk map). The frequent occurrence of higher values may be found, for example, in the following districts: Jindřichův Hradec, Písek, Prachatice, Strakonice, Plzeň - South, Sokolov and Tachov. According to the measurements in 2015 it is possible to make an estimate of the average exposure to radon from water as a consequence of Rn 222 presence (effective dose from ingestion and inhalation) at 0.06 mSv per year.
Duties of water suppliers
Pursuant to the Atomic Law and the Regulation No. 263/2016 Coll.and the Regulation No. 422/2016 Coll., all water suppliers to the public water mains are obliged to secure the systematic measurements and evaluation of radon concentration in drinking water with a frequency dependent on a volume of supplied water. If the radon concentration is higher than 300 Bq/l, water must not be supplied, and it is necessary to reduce radon concentration in water by a suitable remedial measure or to replace this water source. If radon concentration is higher than the guidance level of 100 Bq/l, it is necessary to assess a possible elimination of radon in water (in such a case to compare the cost and benefit of the remedial measures). In 2015, it was found that 0.7 percent of the analysed samples had exceeded a level of 300 Bq/l.
How to remove radon from water?
The aerating equipment is only used to remove radon from underground water in the Czech Republic, that is, radon is removed off water by aerating. There is several hundred of this type of equipment now operating in Czech water treatment plants. Its efficiency is high, normally more than 90 percent. This means that the radon concentration in water is reduced more than ten times; purchase and operating costs of the equipment are about several hundred thousand CZK per a unit, and hence, the equipment is not usually used in small water sources.
Our regulations do not require measuring radon in drinking water used for individual purposes, and hence, no limit has been specified. Only the guidance levels have been specified, and the remedial provisions are recommended in case the following levels are exceeded: up to 200 Bq/l - no measures required; from 200 to 1,000 Bq/l - ventilation of all rooms with a high water consumption (i.e., bathrooms); above 1,000 Bq/l - radon removal from water or a replacement of water sources. Even if the measurement for an individual water supply is not compulsory, it is recommended that the measurement should be done at least in the areas with high radon risk from geological subsoil (see the map). In these areas, there is a high radon concentration probability in water up to thousands of Bq/l.
2. Other natural radionuclides in water
In addition to radon, the other natural radionuclides are present in drinking water; however, in lower concentrations. These are mainly radium (Ra-226) and uranium isotopes (U-234 and U-238). They enter into water in the same way as radon, and drinking water that contains such nuclides also causes certain exposure to the population.
Determination of natural nuclides in water
The determination of individual natural radionuclides (about several tens of radionuclides) in water is time-consuming and expensive work. Hence, two group indicators were specified, i.e., gross alpha counting and gross beta counting that characterise the content of natural radionuclides (other than radon) in water. The guidance level of 0.2 Bq/l for the gross alpha counting and the guidance level of 0.5 Bq/l for gross beta counting were determined for water that is supplied to the public water mains. If any of these values are exceeded, it is useful to determine the concentration of individual radionuclides in water (and our legal regulations require such measurements).
The gross alpha/beta counting and the measurement of the concentrations of the individual natural radionuclides in water are done in a laboratory. The samples of water with a volume of some litres are taken into plastic containers, and immediately after sampling, nitric acid is added. The measurement of natural radionuclide concentrations is classified as the most significant performance from the standpoint of radiation protection, and hence SÚJB permission is needed. About 15 companies have received the permission, and their list can be found on SÚJB web page www.sujb.cz
A mean value for the alpha gross volume activity was equal to 0,059 Bq/l, for the beta one 0,10 Bq/l according to the results of gross alpha/beta obtained in water that was supplied to the public water mains in 2015. The guidance levels were exceeded for 5 percent of the alpha gross activity and 0,3 percent of beta one of the total public water mains number. Based on the measurements in 2015 the average exposure to population at the cost of water use (committed effective dose) on the CR territory through a presence of radionuclides emitting alpha radiation is in the range from 0,001 to 0,004 mSv/year. The guidance level of alpha gross volume activity is exceeded for the most part through presence of uranium in underground water. The concentration of uranium, which is occurred in drinking water, weakly affects the exposure dose. However, uranium is toxic as well as other heavy metals. Uranium content in drinking water is monitored by the Public Health Institutions as well.
The content of all radionuclides present in drinking water is responsible for the effective dose in the average of approximately 0,007 mSv/year in 2015. This result is consistent with the long-term results in the framework of the statistical error.
Duties of water supplies
As well as for radon, and pursuant to our regulations, the suppliers of water to the public water mains are obliged to count the gross alpha/beta in supplied water with a frequency dependent on a volume of supplied water. The more detailed analyses that determine the individual radionuclides in water are required only in case the guidance levels are exceeded. If the result exceeds the values that are specified in the regulation, water must not be supplied to the public water mains.
To assess drinking water, a value named “indicative dose” has been introduced. It characterizes a radiation resulting from water use. Laboratories, carrying out a complete analysis of water, calculate an indicative dose from analysis results. Having exceeded the guidance level, a water supplier is obliged to carry out remedial measures leading to its decrease in cooperation with the State Office for Nuclear Safety.
Removal of natural radionuclides from water
The removal of radon and uranium off water is a time consuming and expensive matter, and the problems are also with the existing radioactive waste disposal. The most suitable solution is to replace this water source. However, there are about 20 preparation plants, using an equipment to remove uranium from water.
As for radon, our regulations do not require counting the gross alpha/beta in drinking water for individual water supplies, and no limit is specified either for the gross alpha/beta counting. There are only the guidance levels, i.e., 2 Bq/l for gross alpha and 5 Bq/l for gross beta. If the guidance levels are exceeded, it is recommended that water be used only as service water.
Suppliers of drinking water and sellers of bottled water may obtain more information on web side of the State Office for Nuclear Safety https://www.sujb.cz/radiacni-ochrana/prirodni-zdroje-ionizujiciho-zareni.