Watchdogs have praised Portsmouth Water’s falling complaints record.
But they say they are concerned by the level of gripes about Southern Water, which operates across most of Hampshire.
Portsmouth Water had the lowest number of written complaints per 10,000 customers which is the lowest in the country.
The figures come from Consumer Council for Water’s annual report, which was published today, and shows the average number of complaints was 33 per 10,000 customers.
Paul Barfoot, head of retail at Portsmouth Water, said: ‘While accepting one complaint is a complaint too many, I am still really pleased we have the lowest level of complaints in the industry.
‘Our overall record sits impressively above the rest of the industry.
‘We take every complaint very seriously and have a complaints and compliment panel that reviews every complaint and compliment received ensuring that we learn the right lessons and always aim to deliver the best customer service possible.’
Neville Smith, managing director, added: ‘Our performance in delivering excellence to our customers is testament to our team of dedicated employees.
‘We must not, however, rest on our laurels and while we are very proud of being the industry leader we are continually looking at ways to improve our service to customers.’
Nearly half of water companies across England and Wales saw an increase in written customer complaints in 2015/16, with some recording ‘alarming’ surges, said Consumer Council for Water.
It has asked four companies, including Southern Water, to report back by the end of October to explain what they are doing to drive down complaints.
For the fourth year in a row, Southern Water was the worst-performing company, having seen a 10.3 per cent increase in complaints compared with 2014-15.
Southern Water received around 77 written complaints per 10,000 connections from customers - more than double the industry average of 33.7.
The company’s director Simon Oates accepted there is ‘still much more for us to do to come in line with the rest of the industry’.
He said: ‘We want to reassure our customers we remain fully committed to continuing the improvements we have already made, and bringing our performance up to the standard they quite rightly expect from us.
‘We are pleased to have the opportunity to report back to CC Water next month, and are confident the figures we submit will show a marked reduction in the number of complaints we have received.’