Thames say that this leap in profits is due to improved efficiency, which has driven down the operating costs by 9.7% (£50M). Pre-tax profits increased to £199.7M.
Capital spend is on course to be the highest on record for a British water company, up by 32% (£478.M) compared to the same reporting period last year, funded by profit and further borrowing - 266km of track was installed over the last six months.
According to David Owens, chief executive officer of Thames Water, "The legacy of high operating costs and inefficient working practices has now been put behind us, and the past nine months have seen the company make huge strides to address the issues which really matter to our customers and stakeholders: tackling leakage, improving customer service and providing consistently excellent water quality.
"Capital investment is up and on track to be at around £1bn, the largest annual investment ever undertaken by a water company. Investment will flow to the number of major projects currently underway, improving security of water supply, addressing leaks and improving wastewater outputs.
"Profits are up on the previous reporting period, to £199.7m, a rise of 49.8%," he said.
The company will publish its Strategic Direction Statement in December, outlining its 25-year plan.