Sewage

Thames Water is the authority responsible for treating and disposing of our sewage 

Sewage from Sandridge is handled by Thames Water as the regional sewerage provider. 

It is processed at the Maple Lodge Sewage Treatment Works, located in Maple Cross near Rickmansworth.  This facility serves much of west Hertfordshire. 

The treated effluent from Maple Lodge is usually discharged into the adjacent Grand Union Canal, but untreated storm overflows or spills from this works, when they occur, are discharged into the River Colne. 

See below for Thames Water's reaction to St Albans housebuilding developments:

In the statutory consultee response to the Shottridge Close proposal, Thames Water informs the Council:

Thames Water has identified an inability of the existing SEWAGE TREATMENT WORKS infrastructure to accommodate the needs of this development proposal. As such Thames Water request the following condition be added to any planning permission.

• No development shall be occupied until confirmation has been provided that either:- 

• all sewage works upgrades required to accommodate the additional flows from the development have been completed; or

• a development and infrastructure phasing plan has been agreed with the Local Authority in consultation with Thames Water to allow development to be occupied. 

• Where a development and infrastructure phasing plan is agreed no occupation shall take place other than in accordance with the agreed development and infrastructure phasing plan.

Reason – Sewage Treatment Upgrades are likely to be required to accommodate the proposed development.

In Thames Water's response to the Woollam Park proposal:

An upgrade scheme is currently being finalised for our Maple Lodge STW to ensure a higher quality of treated effluent, reducing phosphorus levels entering the river to below an average level of 0.25mg/l*. We’ll also increase the capacity of the storm tanks. This will reduce the need for untreated sewage discharges during storm conditions. We currently plan to complete this work in 2030. 

In March 2026 Chris Ward emailed our MP Victoria Collins about the dire situation regarding the sewage treatment works and Thames Water's inability to take any more waste or surface water. Here is her reply:

Thank you for getting in touch and for raising these concerns. You are absolutely right that wastewater and sewage treatment capacity is a critical issue when it comes to planning and housing growth, and it is something I have been raising repeatedly since being elected.

The situation you describe at Maple Cross Sewage Treatment Works highlights a wider problem: wastewater infrastructure often serves large catchments that cross multiple council boundaries, while planning decisions are taken locally and development can proceed faster than infrastructure upgrades. As you note, this can place considerable pressure on treatment works and increase the risk of pollution incidents in our rivers.

Ensuring that development does not run ahead of the infrastructure needed to support it is a key part of the work I have been doing on what I call an “infrastructure first” approach. As part of that work I have recently written again to the Environment Agency, and tabled a number of parliamentary questions asking Ministers about sewer capacity, planning decisions and the impact of new development on storm overflow discharges.

I recently sent an update to residents who have contacted me about chalk streams, sewage pollution and local rivers, which summarises this work and the latest steps I have taken – I hope you too received one? As you will have seen, this includes further action in Parliament and ongoing engagement with both regulators and water companies.

You raise an important point about whether the Government and Planning Inspectors fully consider the capacity of wastewater infrastructure across wider catchments when assessing development proposals. This is precisely the kind of issue I have been pressing Ministers to address, and I will continue to raise it as part of my wider campaign to ensure that infrastructure keeps pace with development.

Thank you again for taking the time to write. Please do keep in touch if you have further information or observations – local insight is extremely valuable in helping me hold both regulators and water companies to account.

With best wishes,

Victoria Collins MP 

Member of Parliament for Harpenden & Berkhamsted
House of Commons, London SW1A 0AA 
Email: victoria.collins.mp@parliament.uk

Many thanks to Team SOS member Christopher Ward for inspiring us to find out where our sewage ends up!