Monitoring for trace elements in drinking water

Drinking water flowing from a tap. istockphoto.com © Michael Bodmann

The BGS has carried out an investigation of the occurrence of trace elements in drinking water in England & Wales on behalf of the Drinking Water Inspectorate (DWI).

The study, conducted during 2010–2013, collated existing data for trace elements in treated water and raw (untreated) water in order to establish the scope of existing data, identify gaps in knowledge and inform the design of a new drinking water survey.

The survey was carried out as part of the project and involved collection of treated drinking water samples from a representative selection of treatment works across England & Wales and tap waters from a selection of consumers' taps.

Testing for a wider range of trace elements

The concentrations of trace elements in our drinking water affect its safety and acceptability for use. Water companies in the UK monitor drinking water regularly for the elements specified in the national Water Supply (Water Quality) Regulations. These elements are: antimony, arsenic, boron, cadmium, chloride, copper, fluoride, iron, lead, manganese, mercury, nickel, selenium and sodium.

Testing for other elements (for example barium, bromine, caesium, cobalt, iodine, lithium, molybdenum, phosphorus, rubidium, strontium, uranium, vanadium, zinc) is less common and typically occurs only when a specific risk has been identified. Data for trace elements not covered by the current drinking water regulations are therefore much more sparse than for those subject to regular testing.

There has been no central reference or collated national database to provide an up-to-date assessment of the concentration ranges and distributions of those trace elements in drinking water that are not covered by the drinking water regulations. This project aimed to provide that point of reference by collation and review of existing data from disparate sources and by conducting a targeted drinking water survey.

Collating data for source waters

Drinking water is derived from a combination of surface water (rivers, reservoirs) and groundwater (boreholes, springs) sources. While the trace element compositions of these raw source waters are not necessarily equivalent to those of drinking water following treatment, they provide a useful indication of the scope of trace elements likely to be present and their distributions.

Data for raw source waters are available from monitoring programmes carried out by the water companies and the Environment Agency, as well as from a number of research organisations (including BGS and the Centre for Ecology and Hydrology). Again, the bulk of the data available relates to elements specified in the drinking water regulations.

Sampling drinking water

The trace element data collated from the various organisations were used as a basis for the design of the new drinking water survey. Water samples collected from treatment works were tested for major elements and a wide range of trace elements. The works were monitored quarterly over the space of a year to assess seasonal variation.

Samples of drinking water were also collected from a number of consumers' taps receiving water from the sampled treatment works. Both flushed and non-flushed (first morning draw) tap water samples were collected and analysed in order to assess any changes in chemistry related to plumbing systems.

Project outcomes

The project results now being finalised will provide the Drinking Water Inspectorate with an improved knowledge base on the occurrence of trace elements in drinking water, which will:

  • provide better information on concentration ranges
  • improve the capability to assess the likely consequences of future changes to the drinking water regulations
  • allow improved estimates of the contribution of drinking water to overall trace element intake
  • provide DWI with a better framework to answer queries on trace elements in drinking water as they arise

Contact

Contact Dr Pauline Smedley for further information