£1.6 billion is going to be spent upgrading sewage treatment works and sewers in the Thames Valley and beyond.
Thames Water is more than doubling its investment over the next two years.
The investment will help Thames Water achieve its commitment to reduce the total annual duration of discharges by 50% by 2030, with an 80% reduction in discharges in particularly sensitive catchments.
Starting in April, £1.12 billion will be spent on sewage treatment plants, including £650 million enhancing and upgrading over 135 existing sites to improve resilience and provide additional capacity.
Thames Water will then spend a further £470 million on the wider sewer network.
Sarah Bentley Chief Executive of Thames Water, said: “The discharge of untreated sewage is unacceptable, and we are committed to tackling this problem. We are investing record sums in upgrading our sewer systems and treatment works and are striving every day to reduce the discharge of untreated sewage into our rivers.
“However, there are no quick fixes. Population growth will increase the strain on our sewage network and treatment centres. And because of climate change, the south east of England is experiencing heavier downpours, which can overwhelm some sewage treatment works. The scale of the challenge demands urgent and systemic reform with a shared undertaking from all stakeholders.”