Birmingham's biggest water supplier has blamed its poor phone system for the near doubling of complaints.
Severn Trent, which is based in Sheldon, has been criticised as being one of the worst in the country by the water watchdog, which unveiled national figures yesterday.
Complaints about Severn Trent rose from 36,239 in 2005/06 to 68,874 in 2006/07.
The company, which recently unveiled a major shake-up including moving its business centre to Coventry, said a third of the figure was for people complaining they could not get through on the phones to complain.
Across the country the Consumer Council for Water found nearly half the complaints were about billing and charges.
Martin Kane, Severn Trent's customer relations director, said: "We are aiming for a 30 per cent reduction in total complaints by next year and are confident our focus on better training and recruitment of skilled staff is having a direct impact.
"Last year, one of the top complaints was about not being able to get through to us on the phone and that accounted for almost one third of all complaints. Already this year we have seen that figure drop to just three per cent."