Welsh Water’s pollution incidents shot up last year, despite the company spending hundreds of millions of pounds to “improve services”.
The company recorded 107 pollution incidents in 2023-24, up from 89 the year before.
Welsh Water has faced criticism in recent months over its performance on leaks and raw sewage spills.
Chairman Alastair Lyons said the company had “still more to do” but was making “good progress”.
Natural Resources Wales (NRW) reduced the company’s rating in June 2023, meaning it “requires improvement”.
Welsh Water did not state how many of the 107 pollution incidents were serious.
The company said it invested £483m last year to “improve services to its customers and communities and to protect the environment”.
However, it also reported 201 sewer flooding incidents, up from 169 the year before, while leaks rose to 251.7 millions litres per day, up from 242.1 million.
The company said it had agreed 145 new environmental permits with NRW to remove more phosphorus from its treated water before it is put back into rivers.
Mr Lyons said: “Our plans have to find the right balance of being financeable, deliverable and affordable for our customers without storing up problems for future generations.
“Whilst there’s still much more to do, we are making good progress against the commitments we’ve made.”
It comes after an anticipated review of how expensive water bills could be over the coming years was pushed back to 11 July because of the general election – it was originally pencilled in for 12 June.
The consultation will see Ofwat give its initial verdict on water companies’ business plans until the end of the decade, which it does every five years.
Welsh Water chief executive Peter Perry added: “We are prioritising investment in the storm overflows that cause environmental harm rather than those which spill the most.”
Back in May, the company was ordered to pay nearly £40m to customers after the industry watchdog, Ofwat, found the firm misled them over its record of tackling leaks and saving water.