Disputes over household water usage amounts and estimated bills has driven written complaints to firms up for a third successive year, an annual survey has found.

The Consumer Council for Water (CCW) said it was keeping a "close watch" on Essex and Suffolk Water, which it marked "poor" for both written complaints and complaint handling.

The company has now made commitments to CCW to improve.

Billing problems accounted for 67% of disputes raised by customers in England and Wales, with overall written complaints up 11% on last year to reach a five-year high, the CCW said.

The total was skewed by Thames Water, which was responsible for 42% of complaints the industry received, despite only supplying 19% of domestic properties.

CCW said households had a right to expect clear and accurate water bills and be treated with empathy by suppliers if they slipped into debt, after finding concerns over bills dominated two-thirds of the 93,758 written complaints made to companies in England and Wales during 2020-21.

Customers' frustrations largely stemmed from disputes over how much water they had used, as well as the accuracy of estimated bills and the way some suppliers went about recovering debt.

CCW acknowledged Covid-19 had presented challenges for the industry but noted nine water companies were still able to reduce their written complaints.

CCW chief executive Emma Clancy said: "We're heading into a difficult winter for many struggling households as they deal with rising energy costs and other financial pressures so companies must not allow water bills to add to customers' worries.

"Households have a right to expect clear and accurate bills but water companies also need to improve their communication and do more to understand their customers' needs."

A Water UK spokeswoman said: "While it is encouraging that almost half of water companies have reduced the number of complaints they received year on year, all companies are working hard to bring complaints down, after their call centre capacity was dramatically limited over the last 18 months.

"More than a million households are currently getting help to pay their bills, and that's set to rise to 1.5 million. In addition, during the Covid-19 pandemic, water companies have provided more than 100,000 payment breaks to customers."