Meeting the challenge
When it rains heavily, the sheer volume of water caused by rainfall from buildings and surfaces entering drains and mixing with foul water from homes and businesses can overwhelm the public sewer network.
This can lead to storm overflows operating like a release valve, automatically releasing this heavily diluted mix back into the environment without it being treated at a water recycling centre first to help protect properties from the risk of sewer flooding.
These overflows have always been part of the sewerage network in this country, but we've committed to reducing the impact of untreated water, spending £8.5 million a month over the next five years on improvement schemes.
What we did in Warminster
One of the ways we're investing to reduce the impact of storm overflows is by installing storage tanks, which help us hold the stormwater until a nearby water recycling centre can treat it.
In Warminster, the YTL Construction team – completing the project on behalf of Wessex Water – sunk a shaft 12 metres into the ground on the site of an old petrol station-turned car park in Weymouth Street, close to the centre of the town, in which to house the new 407,000-litre tank.
This included the digging up and removal of redundant underground petrol tanks.
To help with the considerable excavation and equipment needed, one lane of Weymouth Street was closed to through traffic throughout the scheme, with our project team working closely with local customers, businesses and Warminster Town Council to keep them updated and minimise disruption as much as possible.
The excavation proved challenging as the team battled with an influx of groundwater filling up the base of the shaft, which held up progress before a solution was eventually found.
How will it help?
The project was completed in August 2025, and adding this storage capacity is expected to significantly reduce the instances of the nearby storm overflow discharging, helping improve the quality of water in the Were river running through the town.
The new tank will help the local sewer system cope with rapid increases in the flow of wastewater after heavy rainfall, with the stored water initially retained, then safely returned to the sewer system and onwards for treatment at a nearby water recycling centre after the storm has finished.
What else are we doing?
The Warminster project follows similar schemes completed in Wiltshire in recent years, including in Bradford on Avon and Chippenham and, slightly further afield, storage solutions in Bath and South Gloucestershire.
From 2025 to 2030, we are spending £515 million on 143 overflows to reduce their impact on the environment, including 31 nature-based solutions, such as wetlands and reed beds, and increasing treatment capacity at our water recycling centres, separating rainwater and foul water and lining and sealing pipework to prevent groundwater getting into the system.
Find out more about how we're heavily investing throughout our region.