People living in Brighton and Hove face paying more to Southern Water in the summer months.
The company plans to use seasonal tariffs to try to preserve water supplies over the summer.
Customers in Hampshire will be the first to pay the higher summer charge when new water meters are installed.
But the company will then spread the practice across Sussex, including Brighton and Hove.
Water use will be charged at 6 per cent higher than the standard rate from June to September.
The price will be 2 per cent below the standard charge from October to May.
Southern Water chief executive Les Dawson said that most customers would end up paying about the same amount over a year.
With almost half a million water meters due to be installed over the coming five years, the company hopes cost-conscious consumers will be more careful with their water use.
It believes that metering is fairer than water bills being based on the rateable value of a property – the traditional method of billing in Britain.
A Consumer Council for Water survey three years ago, however, reported that just over one in four favoured water meters.
