Thames Water has agreed to accelerate its plans to increase capacity at sewage treatment works and is providing more details about each location on their interactive sewage map.

West Oxfordshire district councillors Lidia Arciszewska, Executive Member for Environment, Charlie Maynard and Alaric Smith and council officers have been working with Thames Water over the past 12 months on steps to reduce sewage pollution in local waterways.

The team has shared some of the details about the ongoing discussions.

The council team were concerned that Thames Water's calculations were 'optimistic'  on data such as the amount of water used by each person that ends up in the sewage system.

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Mr Maynard said Thames Water have now agreed to stop using their "highly inaccurate" set of forecast population data and have moved over to using SOLAR population data.

They have worked with the council's planning team to generate as accurate a picture as possible of future housing growth and forecast population.

On water consumption, he said: "Thames Water was assuming large drops in water consumption by 2025 despite not even starting to be roll out their smart water meters locally until 2025.

"It has now decided to accelerate the smart meter roll-out in West Oxfordshire so that it will be complete by December 2024.

"Thames Water state that smart meters typically reduce consumption by 12 per cent and we’ve asked for data to demonstrate that percentage drop."

The Environment Agency sets the level of flow that a sewage works must treat before passing any to its storm tanks at three times the level of flow it would receive on a dry day. 

Across West Oxfordshire Thames Water is applying multipliers as low as 2.4. It has now agreed to apply a three-times mutiplier to planned works.

On infiltration, the team calculated that 47 per cent of flows through sewage treatment works is from ground and surface water rather than sewage itself.

"Fixing this is a huge task," said Mr Maynard. "We’re working with Thames Water to agree on a set of metrics which will more effectively track progress."

But he added: "Perhaps the best news is that Thames Water has agreed to accelerate its works plan of sewage treatment works capacity increases.

"Some of their planned expansions such as Witney and Bourton-on-the-Water look an appropriate size to accommodate future growth out to at least 2030.

"However, many either aren’t large enough or lack the necessary information to be able to draw a conclusion. We remain on the case."

Thames Water will soon be launching a “fix my sewer” equivalent to “fix my street” and it is deciding whether to change their rules about insisting on visiting sites before doing any work, even in the cases of repeat identical problems.

The status of sewage treatment works has now been added to the council's planning validation checklist to ensure that all development applications declare from the outset whether there is sufficient capacity at the relevant sewage treatment works for the new dwellings.

"Despite months of working on this, their response is still too often 'no problem' when there are obvious problems that they should be highlighting," he said.

When there is insufficient capacity, which is currently the case almost everywhere in West Oxfordshire, a planning condition will be added stating that new homes may not be occupied until additional capacity has been installed.

Buyers and solicitors will be made aware of this condition upfront.

Thames Water and the council continue to negotiate the wording of this clause.