Ofwat has approved price rises for customers of Bristol Water and Dee Valley Water in the New Year, but by less than the companies had asked for.
Prices in North East Wales and the North West of England will increase by 4.4%, whilst Bristol Water customers will pay an extra 2.9% by 2008.
The unexpected rate hike is the result of increasing charges for water abstraction set by the Environment Agency, in addition to rising service costs, with more and more customers choosing to install free water meters.
According to OFWAT, the average water bill in Bristol will be around £144 by 2010.
OFWAT chief executive Regina Finn said: "We will continue to protect the interests of customers by providing a rigorous challenge to monopoly water companies.
Customers of Bristol Water and Dee Valley Water will only pay for the costs facing their companies that are both substantial and meet the strict qualifying criteria," she said.