The science behind bathing water quality testing

Dani Coombes, Environment Protection Officer with the Department of Environment, Food and Agriculture (DEFA), writes about the bathing water quality testing carried out in Manx waters during the summertime:

The Environmental Protection Unit of DEFA collects bathing water samples between the 1st May and 18th September as this is the time where the public is most likely to use the bathing waters around the island.

The Isle of Man has five designated bathing waters – Port Erin, Chapel beach at Port St Mary, Castletown, Douglas Central and South Ramsey – and samples are collected weekly from these locations.

Sampling consists of officers wading into the sea at each location along a pre-determined sampling line to collect a litre of water in a brown glass bottle for analysis. This bottle is stored in a cool box and delivered to the Government Analyst’s laboratory, also part of DEFA.

Sampling is undertaken in most weather conditions and at varying times/tides to capture the variation in water quality.  

The samples are analysed by the Government Analyst for faecal indicator organisms (FIO) specifically Escherichia coli (E.coli) and Intestinal Enterococci. The data is compared against the standards outlined in the Water Pollution (Bathing Water Standards and Objectives) Scheme 2021 which are the same as the EU 2006 Bathing Water Standards. The standards are designed for the protection of public health and the data collected by the Department allows the public to make informed choices on where and when to bathe. The data is uploaded to an Isle of Man Government webpage for the public to access.

Bathing water quality can be impacted by adverse weather as FIO concentrations are likely to increase due to run off from agricultural land and overflows from sewerage infrastructure. 

Monthly monitoring is also carried out at historically sampled sites to provide some data on the bathing water quality; this data can be viewed here.