The company which owns Dwr Cymru/Welsh Water - Glas Cymru - has announced a pre-tax profit of £11m for the last financial year.
Glas Cymru has owned and operated Welsh Water since 2001
The not-for-profit firm, set up five years ago, has no shareholders and will reinvest in the business.
Customers will also each receive a £19 "dividend" in a deduction from bills.
It comes as the chairman of the Scottish water watchdog hinted that the Glas Cymru model might be something that could be adopted in Scotland.
Glas Cymru serves about 2.9m people across a geographical area covering most of Wales.
Its results for the year to 31 March 2006 showed a pre-tax profit of £11m, compared with the £4m profit returned in 2005.
The company said that its "strong financial performance" meant customers would receive an increased "customer dividend" this year of £19.
Finance director Chris Jones said: "We are a private water company like the water plcs but the difference for us is that we are not actually owned by shareholders.
"It means that the profits we make are all retained in the business and that's what enables us to provide benefits to customers like this year a dividend of £19.
"What we've demonstrated that a not-for-profit private company can raise significant amounts of money and do so on favourable terms."
Earlier this week, Sir Ian Byatt, the chairman of the Water Industry Commission for Scotland, suggested in an interview with The Scotsman that Scottish Water could follow the Glas Cymru model and set up as a not-for-profit body or as a cooperative.
But Mr Jones said it may not be suited for conditions elsewhere.
He added: "I don't know whether this would work in Scotland or indeed elsewhere, but it seems to have worked so far in Wales."
Glas Cymru chairman Lord Burns said the company's financial performance had "exceeded our expectations".
He added: "It is now just over five years since Glas Cymru became responsible for Welsh Water.
"Much has been achieved in that period, but we and our partners remain committed to delivering further improvements in value for money to our customers in the years ahead."