Catchment Management


Dealing with challenges that impact on water quality at source is a more sustainable and cost effective approach than relying solely on intensive water treatment, which uses energy and other resources to remove pollutants.

Our Catchment Management Team works proactively to identify potential sources of pollution and regularly monitors rivers and groundwater in our communities. We also undertake a wide range of investigations with the Environment Agency and neighbouring water companies.

We work in partnership with local environmental groups and a number of catchment partnerships raising awareness of any issues which could affect drinking water quality. We also work with our communities to find innovative ways to reduce pollution at source, by preventing the pathways that could cause pollution to get into untreated water. Rather than relying just on engineered solutions, we believe in working with the environment through natural methods and working with others to build resilience.


Diagram showing how pollution can enter groundwater and rivers and is then treated at the water treatment works.


River and groundwater monitoring

Understanding where pollution is coming from is a key component of our catchment work. We carry out frequent river and groundwater monitoring for a range of pollutants including pesticides and nitrates at strategic locations to help us understand the source and pathways of pollution which might affect the quality of untreated water. The data we gather helps us identify areas where we can focus our activities and work with potential polluters to find solutions that benefit everyone.


Catchment risk assessments and land use surveys

To maintain a wholesome supply of drinking water to all our customers, our Catchment Management Team carries out detailed risk assessments within each of our water catchment areas. Utilising the Environment Agency - Groundwater Source Protection Zones (SPZ) we identify surrounding land uses, such as industrial, residential and agricultural.

We capture potential risks from those land use types and assess the risks to ensure we have effective treatment in place. Where potential issues are identified, we work collaboratively with our communities to reduce the risk to untreated water quality and the environment. This supports our obligations to develop a source to tap risk assessment, known as drinking water safety plans for all of our water treatment works.


Partnership working

Working closely with our communities is at the core of our business. Our Catchment Management Team collaborate with a wide range of partners, from neighbouring water companies, the Environment Agency, Natural England, local businesses and environment groups to identify ways to improve the natural environment. We are actively looking to promote pollution prevention, by raising awareness of how domestic, industrial and agricultural activity can affect untreated water quality.

We have worked closely with the Environment Agency to identify areas from where we abstract water that are sensitive to pollution risks (Environment Agency: Drinking Water Protected Areas (DrWPA)) and through our catchment investigations, certain drinking water catchments have been designated as Safeguard Zones where we focus our activities. Our plan is to work in partnership with businesses and local communities in order to identify and implement catchment solutions.

In addition, we also support water industry research to further enhance the way in which we manage risks through better technology at the source, in the catchment and at our treatment works.


Natural England Catchment Sensitive Farming (CSF)

Mimmshall Brook Project



This project commenced in 2011 and was set up with local farmers, Affinity Water and Natural England’s Catchment Sensitive Farming initiative to address some of the issues relating to agricultural pollution which was affecting our local water abstractions.


Our investigation

The treatment works in the catchment uses water which is abstracted from the underground chalk aquifer, which is treated to meet drinking water standards and supplied to the surrounding community. Due to the karstic (fractured chalk) nature of the geology in this area, the groundwater is influenced by heavy rainfall and subsequent diffuse pollution from agriculture.

This can result in the following:


Key issues

  • Groundwater can be influenced by heavy rainfall resulting in catchment pollution from farming products

  • Increased usage of water treatment works

  • The need to import water from other areas when pollution levels are high


Possible impact

  • Increased pollution means deterioration in untreated water quality

  • Intensive and costly Water treatment






Our Water Production Manager with some local farmers explaining some of the treatment needed for pesticides and other organic matter at our water treatment works.



Our involvement

Our Catchment Management Team has been working closely with local farmers on this project since 2011 to identify land management solutions in order to prevent catchment pollution, improve untreated water quality, while maintaining crop yields, help manage treatment costs and reduce the need for further treatment.



Colne Community

Zero Metaldehyde pilot project in the Mimmshall Brook


Metaldehyde is the active ingredient contained within slug pellets that are used by UK farmers to control slugs while growing a variety of crop types. Levels of metaldehyde have been detected within surface water systems since measurements of this substance began in 2008.


Whilst the metaldehyde levels detected pose no danger to human health or the environment, breaching the EU Drinking Water Limit of 0.1μg/l must be avoided and water companies must aim to meet their obligations under the Drinking Water Inspectorate (DWI). The aim of this project is to: ‘Develop a consistent and acceptable process of identifying specific geographical locations at which to target specific measures to reduce the metaldehyde input in water catchments’.

Our Investigation

To investigate ways to reduce diffuse metaldehyde pollution at the source, we have established a Zero Metaldehyde pilot project with the Metaldehyde Stewardship Group, Natural England’s Catchment Sensitive Farming initiative and a number of other water companies to help with this project.

Our Involvement

The Mimmshall Brook catchment close to Potters Bar and Borehamwood in Hertfordshire was chosen for the pilot, along with three other catchments nationally. A standard set of high-risk field maps were produced for individual fields, based on the three key elements of soil run-off/leaching potential, field slope and proximity to a watercourse.

The high-risk field map showed the high-risk fields in the catchment and farmers in these areas are being asked to voluntarily use an alternative to metaldehyde on these fields. The pilot commenced in 2014 and will run until 2016. For more information please visit



Colne Community

ColneCAN Partnership

The Colne Catchment Action Network Partnership (ColneCAN) was established in 2011 and is hosted by the Chilterns Chalk Stream and Thames Valley Groundwork’s. The ColneCAN ties together the work of the Colne Valley Regional Park and the Chilterns Chalk Stream Project with the wider catchment. ColneCAN brings together water companies, local authorities, charities, anglers, conservationists, other stakeholders and local residents to ensure catchment-wide thinking and local action.

We are working closely with local environmental groups and, more recently, a number of catchment partnerships in the Colne catchment. Our catchment management team regularly monitors the River Colne and its tributaries for untreated water quality and undertakes a wide range of surveys and activities, to help us understand the potential impacts of pollution on our water abstractions.


River Monitoring

Our Catchment Team undertakes routine river water quality monitoring at strategic sites along the rivers in the Colne catchment to help us understand the source and pathways of pollution which could enter our water abstraction.


Catchment Risk Assessments and Land Use Surveys

Our Catchment Team undertakes risk assessments for each source of abstraction using Environment Agency groundwater source protection zones to identify surrounding land uses (such as industrial, residential and agricultural), their associated pollutants and the potential impact to our abstractions and treatment processes. This helps us to understand the local catchment, the source and pathway for potential pollutants, as well as any potential impacts on our abstractions.


Partnership working

Our Catchment Team works closely with a wide range of partners, from neighbouring water companies, the Environment Agency, Natural England and local environment groups to identify ways to improve water quality. We strongly support and work alongside the Colne Can Catchment Partnership.

In addition, we also support water industry research to further enhance the way in which we manage risks, through better technology at the source, in the catchment and at our treatment works.



Colne Community

Colne Valley Park and Community Interest Company

Affinity Water is proud to be a Corporate Supporter of the Colne Valley Park Community Interest Company (CIC). The Colne Valley Regional Park covers 111 square km from Rickmansworth in the north to Staines in the south, Uxbridge and Heathrow in the east to Chalfont and Slough in the west. It is the first piece of countryside to the west of London and includes over 70 lakes, 200km of rivers and canals, eight country Parks and other visitor access hubs, 19 nature reserves, 13 SSSI’s and a 270km network of footpaths and bridleways connecting it all together. Our landholdings stretch throughout the Regional Park from Stockers Lake to Wraysbury Lakes and we are keen to support the CIC to help achieve its core objectives. These include:

  • To maintain and enhance the landscape, historic environment and waterscape of the Park in terms of its scenic and conservation value and its overall amenity

  • To safeguard the countryside of the Park from inappropriate development. Where development is permissible, it will encourage the highest possible standards of design

  • To conserve and enhance biodiversity within the Park through the protection and management of its species, habitats and geological features

  • To provide opportunities for countryside recreation and ensure that facilities are accessible to all

  • To achieve a vibrant and sustainable rural economy, including farming and forestry, underpinning the value of the countryside

  • To encourage community participation, including volunteering and environmental education

  • To promote the health and social well-being benefits that access to high quality green space brings

For more information, please visit:

Affinity Water staff being recognised as being founding supporters of the Colne Valley Park CIC.


Dour Community

East Kent Catchment Improvement Partnership


The East Kent Catchment Improvement Partnership (CIP) followed on from the East Kent Catchment Improvement Group (CIG) with funding made available from DEFRA in winter 2013/14 to develop the partnership. The East Kent CIG was initiated and administered by the Environment Agency, the first meeting being in August 2011. The CIP follows an integrated catchment based approach to deliver the Water Framework Directive objectives.

Geographic coverage

Many of the challenges facing our water environment are best understood and tackled at a catchment level – the Catchment-Based Approach (CaBA). There are 93 catchments in England. The Water Framework Directive Management Catchment covered by this partnership is the Stour Catchment, within the South East River Basin. The East Kent CIP includes the catchments of the River Stour, Dour and Oyster Coast Brooks, North & South Streams and the Chislet Marshes. This incorporates parts of Ashford, Canterbury, Dover, Maidstone, Shepway, Swale and Thanet local authorities.

Strategic Vision

The East Kent CIP brings together partners to work collaboratively, applying the catchment-based approach, to improve the health of surface and groundwater bodies. The collective Strategic Vision of the Partnership is:

  • We will work together to ensure the health (quality) of water bodies (surface and ground) in East Kent is continually improved so that by 2027 they are all ‘Good’ status / potential as required by the Water Framework Directive. In the short term, we will collaborate to ensure that none of our rivers are ‘Bad’ status / potential by 2015

  • The aim of the East Kent Catchment Improvement Group is to improve the local water environment so that there are multiple benefits including: more wildlife habitat, to protect water abstractions (surface water and groundwater), reduce flood risk, promote sustainable farming, as well as tourism; better recreation opportunities, cleaner bathing beaches; lower water bill rises and a better chance to adapt to climate change

  • The partnership also aspires to involve local organisations, communities and businesses in the identification of realistic, sustainable solutions, securing funding and carrying out agreed actions



Lee Community

Lea Catchment Partnerships

The River Lea and its tributaries - the Mimram, Beane, Ash, Rib, Quin and Stort - drain over 1,000 km2 of Southeast England. These rivers include rare and precious chalk streams, canals and navigations, and urban watercourses. There are several catchment partnerships made up of people and organisations such as landowners, local community groups and charities, councils and government agencies which are working to improve these rivers for people and for wildlife. The partnerships were formed between 2012 and 2014.

Each partnership is ‘hosted’ by one organisation, whose role is to organise and co-ordinate the many different members of the partnerships, as well as develop a catchment plan and drive the objectives forward. They also act as the initial contact point for any enquiries about each catchment and arrange the regular catchment partnership meetings and workshops.

Over the next five years we will undertake environmental improvements on these rivers. We currently sit on the steering groups for the various partnerships and work closely with the catchment hosts and the communities they serve. The main aims of the Lea Catchment Partnership are to improve water quality, manage flow, control non-native invasive species and improve wildlife corridors. The partnerships also aspire to involve people in their local water bodies and achieve improvements by working together.

For more information about the various Lea Catchment Partnerships or to get involved, please visit



Wey Community

Thames Catchment Management Steering Group (TCMSG)

The TCMSG was formed in 2010 by Affinity Water, Thames Water and South East Water to jointly investigate the impacts of metaldehyde and other pesticides in the Thames River Basin District.

All three companies have agreed a programme of work with the Drinking Water Inspectorate (DWI) to work with landowners, farmers and agronomists to identify solutions to reduce metaldehyde. Since its formation, the TCMSG has developed a combined river sampling programme which covers most of the 16,000km² of the Thames River Basin District. The river sampling helps to identify hot-spot areas where pesticide concentrations are highest, and develop consistent messages and investigate catchment-based solutions to prevent metaldehyde and other pesticides getting into surface waters at the source, rather than relying on complex and expensive treatment at our water treatment works.

Every year the TCMSG hosts a workshop for key stakeholders including the Drinking Water Inspectorate (DWI), the Environment Agency (EA), Natural England, the Health and Safety Executive, agronomists, Campaign for the Farmed Environment and pesticide manufacturers and distributors. These annual stakeholder events are an opportunity for the TCMSG to update on the pesticide sampling programme, present progress on projects like our Zero Metaldehyde pilot in the Mimmshall Brook, and discuss issues impacting on untreated water quality in an open forum.

Affinity Water Catchment Management Manager engaging with the TCMSG at the annual workshop.