Welsh Water bills rise 3.8%, with Severn Trent up 5% and Dee Valley 5.4%
Welsh Water says its customers will see an average rise in their bills of 3.8% when charges go up in April.
It says it is the lowest average bill increase of all water and sewerage companies in Wales and England.
Other water companies also have customers in Wales, and regulator Ofwat says Severn Trent bills will rise an average 5%, and Dee Valley 5.4%.
The Consumer Council for Water said many customers were already struggling to pay their bills.
Dame Yve Buckland, chair of the council, said water companies were allowed to add inflation to price limits agreed with Ofwat.
"We will be working with companies and the regulator throughout the next price review to ensure that future water prices are acceptable and affordable," she said.
"In the current economic climate, many customers are struggling with rising household bills and the level of water debt is growing.
"Companies need to tell their customers very clearly what they are getting for their money and to help customers who are having difficulty paying their bill."
Bills across Wales and England will see an average rise of 5.7%.
Welsh Water managing director Nigel Annett said it was investing £1.4bn to improve its infrastructure over the five years to 2015.
"We are working to give our customers the best possible value for money service, while providing the highest quality tap water, reducing the risk of sewage flooding, and protecting our environment," he said.
"The investment to protect coastal waters and rivers has helped gain Wales a third of the UK's Blue Flag beaches, while our rivers are the best in the UK."
He said help was available for those having problems paying their bills.
Benedict Fisher, head of communications for Ofwat, said: "Inflation is running higher than average at the moment so the main thing driving this bill increase is inflation.
"Water companies are monopolies - water company customers can't shop around for water so our job is to make sure customers are protected and part of that protection is to maker sure the prices companies charge is limited."