Households in parts of Kent are facing a bigger hike in water rates than anywhere else in the country.

South East Water customers in the former Mid Kent Water area will see their bills increase by 7.9 per cent – an average of £13 a year to £171.

The hefty rise, which is 4.9 per cent above the rate of inflation, is the largest across England and Wales and comes into effect on April 1.

Customers in the rest of the South East Water area will see a hike of just the level of inflation, which is currently running at three per cent, taking the average bill up £5 to £169.

And those served by Southern Water will see bills rise by 5.6 per cent, an average annual increase of £4 to £127.

However, the picture is brighter for Folkestone and Dover Water customers, who can expect their bills to fall by 0.3 per cent (according to projected figures from Ofwat), meaning an average decrease of £1 to £182.

Thames Water is yet to finalise its 2009 prices.

South East Water said the increase would help fund its £350million investment scheme.

Managing director Paul Butler said: "While the majority of our investment is funded by borrowing, bills do have to rise, in agreement with Ofwat, to help fund our water supply operations.

"Nevertheless we remain focused on keeping these increases to a minimum to help ensure the cost of that service remains excellent value for money."

The company said it will have invested nearly £300million into its pipe network, pumping stations and treatment works since 2005, and is planning to spend another £60million in 2009 and 2010.

In a 2004 agreement, regulator Ofwat set down limits on prices water companies could charge between 2005 and 2010.

Ofwat chief executive Regina Finn said: "We needed to make some tough decisions back in 2004 when we set prices. Investment was vital but we needed to balance this with keeping bills down.

"No one wants to see bills increasing, particularly in tough economic times. Yet over the last 20 years we have made sure that this essential investment has delivered very real benefits for us all."

Water bill prices will remain constant until the end of March next year, with rates for the 2010 to 2015 period due to be set in November.