Householders face paying more for their water during the summer after a water company announced plans to introduce a so-called seasonal tariff.
Southern Water customers in Hampshire, parts of West Sussex and Medway in Kent will have new meters installed from June in an effort to preserve water supplies in the hotter months.
Residents will pay 6 per cent more than the standard rate for their water from June to September, and 2 per cent less than the standard rate for the rest of the year.
The West Sussex-based company insisted that average annual water bills would not rise because it plans to drop the price of water between October and May.
The move comes amid concerns about the future pressure on resources through climate change and the projected population growth in the South East.
Officials hope the introduction of a seasonal tariff will discourage non-essential use of water and help customers think more about water-saving benefits.
A Southern Water spokesman said: "These tariffs are set to discourage non-essential use in the summer months when our water resources come under the greatest stress.
"This tariff is not designed to have any impact on a customer's annual bill, providing their water use is typical throughout the year."
The firm has more than 2.2 million customers in Hampshire, Kent, Sussex and the Isle of Wight but the tariff may only be used with a new type of meter known as automated meter reading (AMR).
These are being installed under the programme and are said to be capable of providing more information about water use, including helping to detect leaks.
The company said that the seasonal tariff is not designed to penalise customers, saying that because the winter tariff will go down slightly the charges should even out if use remains steady.
Some 60,000 customers will have the new meters installed in the first year, and it is expected that 487,000 will be fitted in the next five years, meaning 93 per cent of customers will have a meter by 2015.
Seasonal tariffs are being piloted by several different water companies, but Southern Water is the first to introduce it permanently, the spokesman said.