IT is an untapped resource that seems to be the obvious solution for an island thirsty for water.

While Great Britain is surrounded by water on all sides the fear is that the communities within could dry out if nothing is done to tackle the predicted water shortage.

As reported yesterday by the Daily Echo the Environment Agency has ordered water companies to find alternative ways of meeting rising demands rather than drawing from existing sources like the River Itchen in the south.

Water companies including Southern Water are now locked in battle with the agency over how achievable that is without passing on huge costs to the customer.

The water shortage is a problem that has already been identified in London. There, Thames Water has already started building a plant which would see water from the Thames turned into usable tap water.

If the warnings from the Environment Agency are heeded a similar plant could be coming to the south coast with a price tag of £73m. Earmarked for either Millbrook or Fawley the plant would be modelled on the £250m project currently underway in the capital.

Using advanced technology the plant filters down sea water to such an extent that the salt is removed. The technique known as reverse osmosis works by drawing the water from the sea and following a thorough cleanup, repeatedly filtering it to remove the salt particles so that around 80 per cent of it becomes usable tap water.

However, the plan is not without its problems. In a world where the only shoe size that counts is your carbon footprint the environmental impact of such a project is where the controversy lies.

The reason for looking for alternatives to draining the River Itchen is due to fears over the long-term impact on the delicate eco-systems that sustain the salmon supplies and provides wildlife havens.

But instead of celebrating the safeguarding of the Itchen's ecosystem, environmentalists are simply having to shift their battle ground to the bigger problem of global warming.

It is no surprise that as well as a hefty bill for building a running a desalination plant the potential environmental impact of such a project is of equal magnitude.

Such was the concern over how much damage the London plant would do, it was met with fierce opposition from the then mayor Ken Livingston who launched a High Court challenge to the plans. He said that cleaner, cheaper and less wasteful alternatives should be found to avoid the "energy- guzzling and carbon-intensive" operations at the plant.

Concerns were also raised over the impact the concentrated brine would have once it was discharged back into the Thames once it had been filtered out of the water system.

However, in one of his first moves as first citizen Boris Johnson dropped the appeal against the plant that is now firmly underway.

The green light means that the plant, once completed, will be capable of processing 150 million litres of the slightly salty brackish' river water into drinking water for close to 900,000 people a day.

Thames Water told the Daily Echo how the concerns raised by Mr Livingston and environmental groups had been addressed.

Spokesman Don Sharples said: "It has to be remembered that the desalination plant is only part of our response to the water shortage that has been identified long term.

"Along with the plant we are looking at reducing leakage from our network and increasing water meterage across our region which we know will encourage people to use less water. Currently around 20 per cent of our area is water metered and we would be aiming to increase that to around 80 per cent by 2020.

"We are also looking at ways of increasing our capacity to store water to maximise the amount we can hold while we have the wet weather.

"However, even taking these steps we know it still won't be enough to meet the water shortage. That is why the desalination plant is necessary."

He added that the plant itself, which would be operational by 2009, would be run entirely on the reusable bio-diesel fuel- lessening its environmental impact - and only used in times of need.

Despite London's change of heart, environment groups have maintained opposition to such plants and have called on consumers and companies to look at changing their behaviour instead of relaying on expensive technology.

Failing that, legislation should be introduced if necessary to impose water metering at homes across the region, which according to Friends of the Earth is the most wasteful in the country.

"It is a greater emphasis on changing bad behaviour when it comes to wasting water we need rather than an energy intensive desalination plant," said regional campaign co-ordinator, Brenda Pollack.

"We are worried about such plants because of the energy it takes to operate them, it will inevitably impact on the climate change issue. We need year round, year in and year out behaviour change. If people don't make that change then we would look to Government legislation to enforce that."

Consultant on desalination for the World Wildlife Fund Phil Dickie agreed and added: "I wouldn't say we are against desalination per say but I would say that every other option should be exhausted to lessen demand before looking to energy intensive ways of increasing supply."

He added that when looking at building a plant careful consideration had to be given to where it is sited so as not to disturb the delicate eco-systems which sustain the wider marine life.

Mr Dickie added: "The thing I always say when addressing the prospect of desalination plants is if you are prepared to spend multi millions on that technology, what could you achieve if you spent the money on stopping leakage in the existing networks and addressing the wasteful attitude by customers?"

Should the go-ahead be given to the south coast plant, the likelihood of it turning sea into drinking water anytime soon is slim. The plans for the London plant were first put on the table in 2004 and have only just cleared the final hurdle following a public inquiry in 2006 and a High Court appeal. If feelings about the Hampshire plant run as high it could be some time before we are drinking Solent water.

TOMORROW: The likely impact on wildlife of continuing to source water from our rivers