Hampshire householders are among those facing the biggest hike in water charges in the country to pay a massive bill for environmental improvements.

Southern Water wants to increase charges by 45% over the next five years. By 2009, the average bill will rise from the present £247 to £358.

Water company chiefs claim they need the extra cash to pay for a £2bn investment programme-over £1,000 for every household in the region-to maintain and improve services.

Nearly half of this is to pay for environmental improvement schemes, in line with European legislation and demands from the environment Agency. But watchdog, WaterVoice Southern, says customers will be shocked by the bigger bills, which would increase by 7.7% annually for the next five years.

The group is warning that this could cause hardship for pensioners and those on low incomes.

Spokesman, Karen Gibbs, said: "Many people will be shocked by these bills when they land on their doorstep. We are not saying we don't want money spent on the environment, but rather the water company needs to strike the right balance and consider affordability as a issue. We think they should adopt a more modest approach.

"We also think some of the bigger schemes are of national benefit and could have been funded by central tax rather than falling at the door of long-suffering water customers."

The increased charges, set out in the water companies' five-year plan, still have to be approved by government watchdog, Ofwat.

Residents in the New Forest area, who are covered by Bournemouth and West Hampshire Water, face a 12.5% rise from £104 to £117.

However, that figure does not cover sewerage which is provided by a separate company.

Water bills across the country will rise by an average 29% up from £240 to £310 in 2009.

Southern Water's proposes to spend £150m to reduce flooding from sewers as well as address other customer concerns, such as smelly sewage works.

In addition, there will be a huge programme to further improve the quality of drinking water, river and seawater.

Managing director, Stuart Derwent, said: "Our next five years will be dominated by the need to deliver a very large investment programme.

"We have done our utmost to consider the investment plans against the overriding need to moderate prices to customers, but water charges will have to rise to meet the enormous cost."

Ofwat will publish draft decisions on the plans in August. Increases will take effect in customers' bill in April, 2005.