Thames Water is at the top of a league table charting the number of written complaints made to water firms in England and Wales last year, with the number more than doubling since 2017, the Guardian has reported.

The number of written complaints received by the firm from household customers has risen from 17,039 in 2017/18 to 40,060 in 2021/22, according to the most recent figures from the Consumer Council for Water (CCW). The firm accounted for nearly half (47%) of all written complaints to water and sewerage firms in England and Wales last year.

The Observer revealed last week how a 98-year-old woman with end-of-life care was sent a bill by Thames Water warning that she had used the equivalent of more than a million cups of tea over six months. The usage was later found to have been caused by a leak.

Thames Water had 68 complaints per 10,000 connections last year, compared with Wessex Water which had 10 and Anglian Water which had 17. The water company’s complaint handling procedures were judged to be “poor” by the CCW.

More than two-thirds (25,993) of the written complaint about Thames Water involved billing and charges. It also received more than 14,000 complaints about water supply and sewerage service.

Southern Water received the second-highest number of complaints. The number of written complaints received by the firm has increased from 6,259 in 2017/18 to 9,131 in 2021/22. Its complaint-handling procedures were also judged to be poor.

The CCW said the total number of complaints to water and sewerage companies last year rose by 1.5% to 85,238. It said the majority of companies had reduced written complaints, but Thames Water and Southern Water stood out as “poor performers”.

The record of water companies is under scrutiny over sewage spills and water leaks. Ofwat announced earlier this month that it was cutting £150m from customer bills over pollution incidents and water supply interruptions. Thames Water will return £51m and Southern Water will return £28.3m.

Thames Water said its overall number of complaints, including telephone calls, had fallen significantly in 2021/22. Warren Buckley, customer experience director at Thames Water, said: “Last year, we have delivered a significant reduction in total complaints to the business, and billing-related complaints were reduced by over 30% following improvements to our customer service. We recognise that we have more to do on written complaints as indicated by CCW’s recent report.”

Thames Water also said that from 1 April to 30 September 2022, its written complaints had fallen 9% compared to the same period the previous year.

Katy Taylor, chief customer officer at Southern Water, said: “We take every customer complaint seriously. We realise that our performance hasn’t been good enough and are determined to improve.”

The full story in the Guardian can be read here.