Sherborne's Poo. Thames Water replies to our queries about treatment of our sewage

As you know, about eight weeks ago, I submitted an information request to Thames Water through formal channels to understand better what was going on at the Bourton on the Water sewage treatment works, which treats, or should treat, the sewage from Sherborne. This followed some unsuccessful efforts to get data from Thames Water from earlier in the year and significant discharges into the river system of untreated sewage.

After a delay, I today received a reply.

I"m going to choose my words carefully now. I'm disappointed in the formal response from Thames Water. In my personal assessment they have not properly answered the majority of questions. Some of their answers are contradicted by documents they have also submitted to me. For a number of questions, their replies don't answer the questions. For two questions they've claimed an exemption, but very poorly justified their refusal to provide the data. For a number of questions they've provided an answer to an entirely different question.

I'm going to engage with the Windrush Catchment Partnership, of which we are members, and also with the Parish Council to decide on next steps. I think it's likely that we as a group will challenge their response, formally, through correct processes.

The technical documents they've replied with are too long and detailed to sit comfortably in this blog post; however, I'm very happy to provide them to any member of the Sherborne Brook Support Group who requests it. Just ping me. I'll give you all their documentation, and my own detailed fine tooth comb analysis of their response.

The information they have provided has allowed me to make the following interpretations:

1. The upgrade to the Bourton on the Water sewage treatment works was originally scheduled to have occurred by 2023. That has now slipped nearly 5 years, and the completion to functional operation is now estimated to be 2028. A remarkable near 5-year period of extensions, and there is no certainty, given the constant slipping.
2. They have been unable to explain the anomalous discharges of sewage that the Brook Group identified earlier in the year. They are unable to explain what the current capacity of flow rate is at the treatment works.
3. We had assumed there was a single discharge point. The position is more complex, and still unclear. There appear to be at least three: the treated effluent outfall, which discharges to the Dikler under the permit they sent us; a storm overflow at the works, which appears nowhere in that permit; and a separate overflow on the sewer network south of Bourton, which carries excess flow to a land treatment area and then into the Windrush. Only one permit has been supplied to us. We will be asking them to confirm how many discharge points exist and which permit governs each.
4. Previous claims by Thames Water that they have reduced the influx of groundwater infiltration into the sewage system by 35% have no supporting documentation. They cannot provide any justification for that figure.
5. They declined to say what funding is earmarked beyond the current investment period, saying it has not yet been agreed with their regulators. They also confirm that no further work to reduce groundwater getting into the sewers has been done since November 2025.
6. Their published plan says the catchment will meet government storm overflow targets by 2035-2040, but the reply now says 2045-2050 with no explanation. The effort to improve the Bourton on the Water sewage system might not be complete until 2050, 24 years away. That's something they are not explaining and may well be beyond many of our lifetimes. I'm not happy with that, and nor should you be.

This is a painful process, and it has taken the best part of a year for us to get where we are, still an unsatisfactory position. We are learning more, but only by deductions from incomplete answers. While part of me wants to throw my hand up in horror and walk away, I'm going to stick with it and keep chasing. I now know more about sewage treatment than I ever imagined I would. Let me know if you support that process or not. Fundamentally, we're paying Thames Water to treat our sewage, and I have a very low level of confidence that they're doing it properly. I think they need to be held to account. But it does grieve me that they are wasting both their time and mine. All this effort really should be spent on the sewage we pump out of Sherborne, rather than attempting to answer questions and failing to do it. But until we hold them to account, my feeling is this is their strategy.

This is murky, and I don't apologise for the pun. Think about this every time you pull the chain!