Southern Water Still Can't Say Whether Tonbridge's Sewage Works Has Room for the New Homes

Southern Water has told Tonbridge and Malling Borough Council that it can't currently say whether its own sewage works in Tonbridge has enough spare capacity to cope with the borough's housebuilding targets - a gap at the heart of a long-awaited written response to councillors, published on the agenda for this evening's Housing and Planning Scrutiny Select Committee (13 October).

The response answers questions first raised by the committee in July 2026, when members discussed whether foul water drainage capacity could become a constraint on planned housing growth across the borough, citing Wealden District Council's approach to restricting development in catchments where the sewage network is already under strain. Councillors asked Southern Water to set out its position on pollution performance, existing infrastructure, investment plans and treatment works capacity. The reply, dated 1 October 2026, took almost three months to arrive.

Southern Water's five-page letter leads with scale: a £1.5 billion Clean Rivers and Seas Plan running to 2035, aimed at cutting storm overflow releases, and more than £5 million earmarked specifically for Tonbridge and Hildenborough between now and 2030, including new sustainable drainage work at the Priory Mill pumping station and extra storage and treatment capacity at sites including Ham Hill Wastewater Treatment Works.

On the question that matters most locally - whether Tonbridge Wastewater Treatment Works actually has room for the homes being built or proposed around it - the letter is markedly less specific. "Detailed operational information on the exact available spare capacity at Tonbridge Wastewater Treatment Works is not routinely published," Southern Water wrote, adding that it "would need to provide the latest asset-specific assessment separately to give a current and accurate figure." The company says it does factor the borough's Local Plan housing numbers into its own investment planning, and that it would "bring forward the appropriate interventions" should a capacity constraint be identified in future - a commitment conditional on a problem being found, not a reassurance that one doesn't exist.

This isn't the first time water has threatened to hold up housebuilding in the borough this year - it's just a different company, and a different kind of water. In September, Full Council paused the Local Plan over doubts about South East Water's drinking-water capacity, only for the Government to order it to resume the very next day. Tonbridge MP Tom Tugendhat had already warned ministers that South East Water couldn't supply 13,000 of the homes required across West Kent, and Maidstone's council has separately debated pausing housebuilding over water concerns too. Southern Water's letter now raises the same question from the other end of the pipe: not whether enough clean water can get in, but whether there's capacity to treat what comes back out.

The letter does point to one practical tool. Where Southern Water's own modelling finds a development would outstrip network capacity, it recommends the council attach a planning condition requiring that "occupation of the development is to be phased and implemented to align with the delivery by Southern Water of any sewerage network reinforcement required to ensure that adequate wastewater network capacity is available to serve the development." That's close to the kind of "Grampian-style" condition - one that blocks occupation until off-site infrastructure work is actually finished - that committee members said in July they wanted investigated further, as an alternative to a blanket restriction across whole catchments.

The response goes before the Housing and Planning Scrutiny Select Committee this evening at Kings Hill, where members get their first chance to question officers on whether it answers the concerns they raised in July. Southern Water's letter stops short of saying Tonbridge's treatment works is constrained - it simply doesn't yet have the figure to say either way. Source: Tonbridge and Malling Borough Council, Housing and Planning Scrutiny Select Committee agenda, 13 October 2026