Thames Water 5-year plan for 2020 to 2025 – Thame catchment

February 11, 2021

Letter to RTCT from Richard Aylard CVO, Sustainability Director, Thames Water. 22nd January 2021.

Link to download Stakeholder Glossary

I am pleased to say that, following two rounds of feedback from Ofwat and after detailed consideration, the Thames Water Board decided to accept Ofwat’s ‘final determination’.

We have now started to deliver our new 5-year plan, in line with our restated corporate purpose ‘to deliver life’s essential service, so our customers, communities and the environment can thrive’. Our plan focuses on three clear strategic ambitions:

  • delivering brilliant customer engagement,
  • investing in resilient systems and assets and;
  • generating public value.

Now that the details of our business plan have been finalised, I can update you on what is included on both a regional and a local level. Some of the projects described in these plans already have target dates for completion. Where this is the case we have specified the date. In all other cases, you should assume that the work will be complete by 31st March 2025.

Our long-term regional plans

Water companies have always produced Water Resource Management plans (WRMPs), setting out the projected demand for water supplies in their area, over at least a 25 year period, and how they will meet it. In a new development, we have been working at an industry level to build the framework and methodology for comparable plans for wastewater, now known as Drainage and Wastewater Management Plans (DWMPs). These are long term strategic plans which will set out how wastewater systems, and the drainage networks that impact them, are to be extended, improved and maintained,
from 2025 onwards. This is to ensure they are robust and resilient to future pressures, such as population increase and climate change.

Drainage and Wastewater Management Planning

Throughout the first few years of this new funding period (2020-25) we will develop our first DWMP. We will do this through engaging with our stakeholders as much as possible, so that we understand local challenges and include them in our plans. In October we started holding area-specific data sharing workshops, with one workshop for each Lead Local Flood Authority. The Thame catchment partnership were invited to attend the workshop for Oxfordshire, on the 24th November 2020. If you would like any further information on our DWMP please contact the team at

Water Resource Planning – Water Resource Zones

Our supply area covers 13,000 square km, and every day we supply approximately 2.6 billion litres of water to around 10 million people and 215,000 businesses. Not only is our supply area vast but it is also designated as a water stressed area. To ensure a secure and sustainable supply of water for our customers we regularly review and update our Water Resource Management Plan (WRMP), which can be found here: To tailor our
WRMP to our diverse supply area we have divided it into six different water resource zones (WRZs). The Thame catchment is split between the Swindon and Oxfordshire (SWOX) WRZ and Slough, Wycombe and Aylsburys (SWA) WRZ (Figure 1).

Over the next 10 years in the SWOX WRZ we will be rolling out our progressive metering programme with the aim of achieving total household meter penetration in the area of 92% by 2030. The SWA WRZ will also rollout this programme and aims to achieve 87% smart meter penetration of individual household customers by 2030. Metering on household properties provides both a usage benefit, from reduced customer consumption, and a leakage benefit, from the increased ability to detect and repair customer side leaks.

We will continue to promote water efficiency and metering to help customers use water wisely and by March 2025, we aim to deliver circa 8.8 Ml/d benefits through the water efficiency campaign, including smarter home and business visits. Throughout our whole supply area, we have reduced leakage by 10% from 2018/19 to 548 Ml/d, which is 22 Ml/d above this year’s target of 526 Ml/d, largely due to the ongoing impact of Covid-19 on our repair plan. And now of course we need to go further to deliver on the next round of targets.
Here are of our some of suggestions on how to be more water smart:

Our biodiversity plans for the next 5 years in the Thame catchment

Our plan includes a formal performance commitment to deliver 5% biodiversity net gain on 253 of our sites which have been identified as our more important sites for nature. Fourteen of these sites of biodiversity interest are in the Thame catchment:

  • Aston Rowant SSSI (non-operational)
  • Aylesbury sewage treatment works
  • Chalgrove sewage treatment works
  • Chinnor covered reservoir
  • Cuddesdon sewage treatment works
  • Cuddington borehole and pumping station
  • Dancers End SSSI borehole and pumping station
  • Lewknor covered reservoir and borehole
  • Tring sewage treatment works
  • Watlington SSSI
  • Whitchurch water booster station
  • Whiteleaf water pumping station
  • Winchester Wood water pumping station
  • Worminghall sewage treatment works

We have a large biodiversity net gain project due to commence in Spring 2021 to create a permanent wetland/flood plain grazing marsh in land north of Aylesbury sewage treatment works and grassland improvement. We had a site meeting on the sewage treatment works in September 2020 with a number of stakeholders including the River Thame Conversation Trust, the County Ecologist, EA, and members of the local bird group. The size of the project we are proposing is around 2 hectares in size (20,000m2).

  • Approximately 7000m2 will remain as environmentally enhanced wet pasture – will be categorised as flood plain grazing marsh in the DEFRA metric.
  • Approximately 3000m2 will have shallow standing water (less than 0.5m) year-round.
  • Approximately 3000m2 will be slightly raised mounds for nesting/roosting sites.
  • Approximately 7000m2 will receive removed rank turf and become a cultivated lowland wildflower meadow

This project is currently going through a screening opinion with the Council and we hope to be on site in the early Spring 2021, preferably March.

We have already undertaken grassland habitat improvements on Tring sewage treatment works, Whiteleaf water pumping station and Winchester Wood water pumping station by reducing the mowing from monthly cuts to twice a year cuts where possible. We have submitted requests to our grounds maintenance team to reduce cuts on sites Aylesbury sewage treatment works, Lewknor covered reservoir and borehole and Worminghall sewage treatment works which we hope to be implemented in the Spring.

We are negotiating tree and hedgerow planting with our operational colleagues on Winchester wood, Whitchurch booster, Tring & Charlgrove sewage treatment works and Aston Rowant SSSI.

We are currently investigating the opportunity on Cuddington borehole and pumping station.

We will be in touch in due course to confirm our plans, but if you have knowledge of your local Thames Water sites and suggestions for how to improve their biodiversity, even if they aren’t ones listed here, we would be keen to hear from you.

Water Industry National Environment Programme (WINEP)

Alongside all the other water companies operating in England, as part of our environmental obligations we are required to complete a set of actions, requested by the Environment Agency, which form part of the WINEP for 2020 to 2025.

The national WINEP programme aims to help to tackle some of the biggest challenges facing the water environment, from the spread of invasive species and low flows to the effects of chemical and nutrient pollution. The details of the schemes included in the WINEP are available online, for anyone to view and download, see here:

Our WINEP investment can be broadly divided into eight main categories:

  1. Sewage treatment works (STW) upgrades and network improvements – Investment to
    enhance wastewater treatment, increase storage capacity or enhance the network to
    improve or protect the quality of the receiving waterbody.
  2. Monitoring and investigation schemes – Investment to understand better how our
    operational activities may impact on the environment and how these could be improved to reduce this impact, including the effects of abstraction.
  3. Conservation schemes – Investment to meet specific conservation measures to reduce our impact on protected sites or biodiversity.
  4. Investigations into emerging risks – Investment to understand emerging risks facing the water industry such as trace chemical or pharmaceutical residues, microplastics or antimicrobial resistance.
  5. Catchment management activities – Investment to manage pesticides, nitrates and
    herbicides in surface and ground waters through catchment activities.
  6. Alleviating low flows – Investment to investigate or undertake work to alleviate the
    impacts that our abstractions have on low flows.
  7. Reducing environmental impact of river structures – Investment to improve fish
    passage in waterbodies through work on our assets where they have been proven to be a blocker.
  8. Addressing invasive non-native species (INNS) – Investment to investigate and
    implement measures to reduce the risk of INNS associated with our activities.

The table below summarizes the elements of the WINEP in the Thame catchment. For help with the many acronyms, please see our Stakeholder Glossary.

LocationWater/ WastewaterScheme DetailsAylesbury STW Chalgrove STW Chinnor STW Cuddington STW Culworth STW Dorchester STW Dorton STW Forest Hill STW Haddenham STW

Horton-cum-Studley STW Little Milton STW

Long Crendon STW Princes Risborough STW Shabbington STW Stanton St John STW Stewkley STW

Stone STW Tetsworth STW Thame STW Waddesdon STW Watlington STW Wingrave STW Wheatley STW

Worminghall STW

WastewaterMonitoring of FFT:

a)  Investigation of suitability of existing equipment: Chinnor, Dorchester, Dorton, Haddenham, Little Milton, Stewkley, Tetsworth, Waddesdon, Watlington, Wingrave, Wheatley;

b)  Installation of new flow monitoring equipment: Aylesbury, Chalgrove, Cuddington, Forest Hill, Horton-cum-Studley, Long Crendon, Princes Risborough, Shabbington, Stanton St John, Stone, Thame, Worminghall;

•      All sites: Monitoring of the overflow/discharge to storm storage to complement the flow monitoring in a) and b) above

Chalgrove STWWastewater•      Increase the storage capacity to help contain excess flows in wet weather.

•      Investigation to assess the longer-term declines in concentrations of triclosan, which has previously had a usage ban. This monitoring will help us and the Environment Agency to understand if compliance could confidently be expected in the short term, without the need for expensive and carbon intensive treatment technologies while the

concentrations continue to decline as a result of the usage ban.

Chinnor STWWastewater•      Upgrade of the treatment works to increase full treatment capacity.

•      Investigation to identify and understand any sources of Tributyltin in sewage effluent.

•      To investigate and implement load standstill limits for Triclosan

Chilton STWWastewater•      To investigate and implement load standstill limits for Copper (dissolved)Dorton STWWastewater•      Treatment works enhancement to reduce the phosphorous concentration of the STW final effluent, in order to meet good ecological status in the river.

•      Installation of new flow monitoring

equipment, where the flow has not previously been monitored.

Lewknor STWWastewater•      Treatment works enhancement to reduce the phosphorous concentration of the STW final effluent, in order to meet good

ecological status in the river.

The timescale for delivery for each of these schemes is still to be confirmed, as the majority are still at the design stage, but all are funded and will have been completed by the end of March 2025. For some schemes, particularly those aimed at reduction of discharges of storm sewage, there may be different options to deliver the same objective, and confirmation of our approach will be made nearer the time, following more detailed consideration of the various options.

You may be aware that just before Christmas the Environment Agency announced that the Secretary of State for the Environment, Food and Rural Affairs decided to accelerate approval of the ‘amber’ measures in the WINEP in advance of the ministerial approval of the RBMPs. For the Thame catchment this means seven ‘amber’ schemes will be confirmed as ‘green’ in an update of the WINEP in March 2021. The list of schemes above includes the seven additional schemes.

Wastewater networks

Surface Water Outfalls. Throughout this new funding period (2020-25) we will continue with the surface water outfall programme to identify outfalls to watercourses that are suffering from wastewater pollution. These outfalls are diagnosed with widespread sources, which are most likely third-party misconnections.

Misconnections occur when domestic appliances are connected to surface water drains rather than foul waste pipes. Once identified, they are highlighted to the relevant customer and where appropriate escalated to the local authority to ensure they are resolved.

We are extremely grateful to the volunteers who continue to take part in citizen science Outfall Safari programmes to identify and report on suspected polluted surface water outfalls. We would encourage the Thame catchment partnership to consider organising your own Outfall Safari. This link will take you to our guide on how to do so

If you need any help in facilitating an Outfall Safari please let your Thames Water Catchment partnership rep, know as we want to help and might be able to provide volunteer support. Currently we are not aware of any polluted surface water outfalls in the Thame catchment, but this does not mean they don’t exist.

Our surface water outfall programme has historically focused on our most urban catchments where misconnection rates are higher. However, we are expanding our surface water outfall team to improve coverage of the Berkshire/Oxfordshire area helping us to identify and resolve more misconnections in rural catchments. Our surface water outfall team will share more details in the coming months.

Drainage strategies and reducing infiltration. Over the last 5 years (2015-20) we have developed local drainage strategies for the STW catchments impacted by high groundwater as these areas are at an increased risk of sewer and surface water flooding and can lead to treatment works being overwhelmed. In the Thame catchment, drainage strategies have been developed for the Chinnor, Princes Risborough and Watlington sewerage catchments. We have studied the catchments and are now at the intervention stage and have begun implementing the identified long-term solutions. This includes rehabilitating sewers using a leak tight sewer lining technology and patch repairs, investigating options to disconnect or attenuate roof area which is connected to the foul network, and continuing to monitoring the STW catchment and respond to sewer depth monitor alarms.

The Drainage Strategy framework has been replaced by the DWMP process (mentioned above). The DWMP process does not focus on infiltration risk and therefore to ensure we follow a consistent approach we need to adapt our existing drainage strategies to meet the Environment Agency’s Regulatory Position Statement where required. We are using the latest wet winter period to reassess whether we are targeting the right catchments as a priority and are in the process of agreeing these with the Environment Agency.

Catchment Schemes

We are trialling an innovative approach to catchment management through the Smarter Water Catchments programme, working in collaboration with the Evenlode, Crane and Chess catchment partnership networks with the aim to gradually implement this approach across other catchments, from April 2025, if proven successful.

Next steps

Over the coming months we will continue to develop our plans for this funding period. Throughout that process we want to work with the catchment partnership and other interested parties. We will share partnership opportunities where we identify them, but equally we will always consider any offers of assistance.

I trust this is update is helpful and offers a useful insight into the environmental commitments included in our plan for the next 5 years. If you would like further information please don’t hesitate to get in touch with your current catchment rep, Tim Beech, or you can always reach out to our environmental engagement team via

Yours sincerely,

Richard Aylard CVO Sustainability Director

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