Customer complaints in the water industry dropped by almost 12% last year, reaching their lowest level since 2005, according to a report from the Consumer Council for Water.
The annual Complaints Report shows 163,027 written complaints were made to water companies across England and Wales in the year to March 31, compared with 185,140 the previous year.
Complaints have fallen for the fourth consecutive year.
The Consumer Council for Water (CCW) said this showed it had successfully pressured companies to work hard to improve their services and increase customer satisfaction.
While the overall picture was improving there remained areas for concern, with seven of the 23 water and sewerage companies reporting an increase in complaints during the period.
Tony Smith, CCW chief executive, said: "Customer complaints have been consistently decreasing since the Consumer Council for Water started putting pressure on water companies and identifying poor performers.
"Last year complaints fell at almost three times the rate of the previous year (2010/11).
"However, while most companies have made clear efforts to improve their service, there are still some that need to take action to address their high complaint levels.
"While water is currently a monopoly industry, companies must not rest on their laurels and assume that they can get away with delivering poor service."
The most improved company was Dwr Cymru Welsh Water, receiving 58% fewer customer complaints - a drop of almost 6,400 on the previous year.