Thames Water and South West Water have been identified as the lowest-performing water utilities operating across the United Kingdom according to assessments carried out by the Consumer Council for Water.
Both organisations received ‘poor’ ratings across performance indicators examined by the regulatory body.
In contrast, Portsmouth Water and Bristol Water achieved ‘good’ ratings across both measurement categories, maintaining their positions at the summit of industry rankings as the sector’s leading performers.
The evaluation methodology relied upon the volume of grievances lodged against each provider relative to every 10,000 households within their operational areas.
The publication of these findings follows an unprecedented surge in complaints received by the regulator, which recorded the largest year-on-year increase since its establishment two decades ago.
This escalation coincided with the most significant rise in customer charges since the industry’s transition to private ownership.
Despite the poor assessment, Thames Water has committed to enhancing the service standards delivered to its customer base.
The utility, which serves the majority of Oxfordshire, is among five providers granted provisional approval to implement further bill increases covering the period from 2027 through 2030.
The additional firms in this group comprise Severn Trent Water, Southern Water, Wessex Water and South East Water.
The CCW documented an 84 per cent rise in household complaints, marking the most substantial annual increase recorded throughout the watchdog’s entire operational history.
Separately, grievances submitted directly to water companies by customers surged by 56 per cent compared to the previous twelve-month period.
David Bird, Retail Director at Thames Water, expressed regret that certain customers had not experienced the standard of service they were entitled to expect.
He acknowledged that confusion surrounding billing had proven particularly vexing for consumers, prompting the introduction of a comprehensive redesign initiative aimed at improving clarity.
While acknowledging that tariff adjustments implemented previously had generated substantial correspondence, he emphasised that these revenues had facilitated what he described as the most extensive network modernisation programme in 150 years, including a record capital allocation of £2.7 billion during the 2025/26 financial year directed toward infrastructure improvement, pollution reduction and environmental preservation.
He noted that this year’s household tariff increase had been substantially more modest at 3.4 per cent, reflecting general inflation levels.
He welcomed the CCW’s assessment and indicated the organisation would utilise its conclusions to drive continued service enhancement.
A representative for Water UK, speaking on behalf of member companies, acknowledged that tariff increases were never popular but stressed that investment was essential to fund critical improvements ensuring water supply security, supporting economic expansion and eliminating sewage discharge into rivers and coastal waters.
The representative highlighted that the overwhelming majority of complaints, totalling 94 per cent, were being resolved at the earliest opportunity without requiring escalation to the consumer body.
Environment Secretary Angela Eagle stated that she shared the frustrations expressed regarding the situation, noting that customers had endured unacceptable levels of escalating charges alongside inconsistent service reliability for an extended period.