# The Bathing Waters (Classification) Regulations 1991, Paragraph 3


All samples must be taken at the same point at the place in the particular waters where the daily average density of bathers is at its highest,and preferably 30 centimetres below the surface, except in the case of samples for testing for mineral oils, which must be taken at surface level.

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Source: https://www.legislation.gov.uk/uksi/1991/1597/schedule/2/paragraph/3 (the official version)
Page: https://openlegislation.uk/bathing-waters-classification-regulations-1991/schedule-2/paragraph-3
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.