Catchment management

About 80% of the water we supply comes from groundwater sources in Wiltshire and Dorset. The remaining 20% comes from surface water reservoirs which are filled by rainfall and runoff from the catchment.

The water we provide has to meet drinking water standards which state specific limits on a number of pollutants including nitrates and pesticides.

While rain falling on the catchments is clean, the quality of the water abstracted from our sources is influenced by land practices in the catchment such as the use of nutrients and pesticides. These chemicals are mostly, but not always, derived from agriculture. 

The traditional way of dealing with these impurities is to build large treatment works but these are expensive to construct and operate and do not benefit either the environment or customers.

Since 2005 we have chosen to use catchment management because it:

  • is more cost effective and sustainable
  • offers wider environmental benefits
  • involves working with the local community to tackle these problems at source rather than at the end of the pipe.

Dealing with the source not the symptoms

Catchment management involves us working with local farmers in the catchment areas of public water supply boreholes and reservoirs. 

The methods we use include data sharing, advice, practical help and compensation, where appropriate.

Between 2015 and 2020 the catchment team will cover 20 at risk catchments across our region including:

  • 15 groundwater sites for nitrate (one of these for pesticides as well)
  • five reservoirs at risk from pesticides (including metaldehyde) and nutrients which encourage excessive algal growth.

In addition, our Streamclean team works in urban areas to reduce environmental pollution by tracing and rectifying misconnections.

As a result of this work we've not had to install treatment at any of the sites where we engage in catchment management – nor do we have any plans to do so.

We are now developing our work in other areas including a major new project to offset nitrate entering Poole Harbour from Dorchester sewage treatment works.

Reporting on our work

For the last two years we have produced a catchment report outlining work to improve the water environment as well as activity related to biodiversity, waste management and greenhouse gas emissions.

We have also produced an interactive map that profiles projects in each catchment

River Tone, Parrett and Yeo Phosphorus reduction scheme

Working with farmers in the River Tone, Parrett & Yeo catchments to reduce phosphorus runoff from fields, tracks and farmyards

River Stour phosphorus reduction scheme

Working with farmers in the River Stour catchment to reduce phosphorus runoff from fields, tracks and farmyards

Nitrogen offsetting project

This project aims to offset the nitrate contained in effluent discharged in Dorchester.


We are working with farmers in 15 catchments to improve water quality.

Surface water

We are working with farmers based inside Drinking Water Safeguard zones.


Our innovative trading platform enables farmers to bid for funding.

Contact us

For more information about our catchment management work, please email:

Paul Stanfield, Head of Catchment Services -

Tim Stephens, River Stour phosphorus reduction scheme and River Tone, Parrett and Yeo phosphorus reduction scheme -

Ben Hunt, catchment management in groundwater and surface water catchments -

Adrian Moore, Poole Harbour nitrogen offsetting project -