Swindon's water provider ranked among worst for complaints
The report about Thames Water has come from The Consumer Council for Water
Southern Water and Thames Water were the "standout poor performers" driving customer complaints over the past year, a watchdog has reported.
The Consumer Council for Water (CCW) said the more than 20 million people served by Thames Water and Southern Water were being "let down" by the two firms' "failure to understand and deal with the causes of high levels of complaints from their customers".
CCW said the industry's overall performance was skewed by the number of complaints made by households to Thames Water and Southern Water.
Complaints received by Southern Water were almost three times higher than the overall average for water and sewerage companies, while Thames Water's were just over one-and-a-half times higher.
Thames Water was the only water and sewerage company to be marked as poor for both the number of complaints it received and its complaint handling.
It was also the worst performing company for billing disputes and the number of complaints that could not be resolved at the first time of asking.
Southern Water was the most complained-about company, with the rate of complaints per 10,000 connections almost twice as high as Thames Water, while it was rated worse than average for how these were handled.
Among the smaller water-only companies, South East Water scored poorly for both the number of complaints it received and how these were handled, and Cambridge Water generated three times as many complaints to CCW than last year.
Among the best performers were Wessex Water, Hafren Dyfrdwy, Bristol Water and Portsmouth Water.
Overall, households made 232,817 complaints to water companies in England and Wales during 2022/23, with problems relating to billing and charges accounting for almost half (47%) of them.
Issues with water services made up 30% of complaints, with these rising significantly during the summer drought of 2022, when six suppliers introduced hosepipe restrictions.
Some 22% of complaints were about wastewater services, falling as a proportion due to fewer instances of extreme wet weather and flooding incidents during the winter months.
CCW said it had seen a 29% rise in complaints brought to it after water firms had been unable to resolve them during the first quarter of 2023/24 compared with the previous quarter.
CCW chief executive Dr Mike Keil said: "Trust in the water sector has never been more fragile and the task of rebuilding it is made all the more challenging when companies perform as poorly as Thames Water and Southern Water.
"We're especially concerned that these two companies have not performed well across all the main causes for people to complain and that Thames, in particular, is compounding customers' frustrations with delays and a failure to resolve many issues first time.
"Customers have a right to expect better from such an essential utility provider where switching supplier is not an option."
Thames Water retail director David Bird said: "We've been working hard to turnaround our performance and have reduced our total household complaints by 28% compared to last year alongside a large reduction in telephone complaints.
"We've completed the onshoring of our customer service call centre in Swindon so we can be closer to our customers and deliver the reliable and better-quality service they deserve.
"We are also investing additional resources to improve our response times to customers and to reduce the need for second-stage complaints.
"Our aim is to always deliver brilliant customer service and we're determined to do better."
Meanwhile, Katy Taylor, chief customer officer at Southern Water, said: "We recognise that we need to do better at serving our customers and fixing their problems.
"We are investing in video diagnostics, upskilling our customer service agents and keeping our customers regularly informed when issues take longer to fix.
"While we are seeing early signs of improvement in the quality and speed we deal with their queries, we know we still have a lot of work to do and are committed to significant improvements."
A Water UK spokeswoman said: "Companies worked hard last year to support customers and maintain infrastructure through an unprecedented drought and record-breaking temperatures, and it is good to see that complaints to the ombudsman remained stable.
"Complaints about bills are increasingly being resolved by companies themselves, with an 8% reduction in these types of complaints being escalated to CCW. However, we appreciate that many customers remain concerned about their bills, which is why we have announced plans to more than double the number of households eligible to receive support, rising to 3.2 million households."