Water bills are set to rise by more than 20 per cent in the next five years.

More than 390,000 homeowners in Sussex can expect bills from Southern Water to go up by an average of £13 from next April.

By 2010 water charges will have risen by more than 20 per cent from £90 to £110 as customers foot the cost of maintenance across the network.

The rise was announced by industry regulator Ofwat yesterday, signalling an average increase of 18 per cent for homes across the UK.

An Ofwat spokeswoman said: "These prices are going to be unwelcome but we have a duty to ensure water companies can provide a proper water and sewage service."

Suppliers had appealed to Ofwat for a 29 per cent increase in their costs in the next five years, with Southern Water calling for more than 38 per cent growth in the billing price limit.

Water bosses highlighted more than £1,600 million of planned works and said higher quality water standards had also triggered rising costs.

Southern Water managing director Stuart Derwent said: "The scale of this work is enormous - approaching almost £900 for each property. It will enable us to make larger inroads into preventing flooding from sewers.

Southern Water customers using water and waste services face an increase of more than 28 per cent for the average bill by 2010.

Consumer watchdog chairman at WaterVoice Southern, Richard Sturt, said: "It is essential any measures the Government proposes to address the impact of bill rises on low and fixed income customers are effective."