This part of ISO 13164 gives general guidelines for sampling, packaging, and transporting of all kinds of water samples, for the measurement of the activity concentration of radon-222. The test methods fall into two categories: a) direct measurement of the water sample without any transfer of phase (see ISO 13164-2); b) indirect measurement involving the transfer of the radon-222 from the aqueous phase to another phase (see ISO 13164-3). The test methods can be applied either in the laboratory or on site. The laboratory is responsible for ensuring the suitability of the test method for the water samples tested.