Bottled-water companies are preparing to take on the soft drinks industry in an attempt to rescue flagging sales.

More than a billion litres of bottled water were drunk in Britain last year, but sales in an industry worth £2 billion in 2006 are falling steeply, with 9 per cent wiped off the balance sheet in the past two years alone.

As the bottled-water industry faces up to having lost its perceived superiority over tap water, leading water brands — including the producers of Evian, Volvic and Perrier – have created a new organisation, the Natural Hydration Council (NHC). That is now working behind the scenes on a new demographic: coaxing soft-drink drinkers over to bottled water.

Years of campaigning from tap water advocates have portrayed bottled water as expensive and morally unacceptable. In the water wars, mineral water’s reputation has been diminishing almost as fast as its sales. On Tuesday, Ralph Searle, of Coolwater Enterprises, will face Cardiff Crown Court on charges of taking tap water from a Welsh industrial estate and allegedly selling it on, claiming it to be mineral water from the Duke of Marl-borough’s Blenheim Palace spring.

As a riposte, the NHC plans to revive the “eight glasses a day” campaign to try to mend the damage done to the industry by a series of bleak summers and economic meltdowns.

Trevor Datson, of Danone Waters, co-founder of the NHC with Highland Spring and Nestlé Waters, said: “All drinks sales are weather-dependent and we’ve had two very poor summers. Also, there is a perceived equivalence between tap water and natural mineral water, which is something we would strongly differentiate.”

The manager of the NHC, Amy Finlayson, says that it was founded because bottled water has been “vilified” by environmental campaigners. Campaigns including London On Tap and Tap Into WaterAid have sought to establish tap water as a cheap, environmentally sound alternative to bottled water, especially in restaurants and bars. Tap water campaigners have pointed to piles of plastic bottles littering beaches and choking landfills, and asked if we could turn our noses up at tap water when so much of the world faces dehydration and disease because of a lack of clean running water.

In response, bottled-water companies would tell us that our tap water had been through nine other people before it reached our glass, and talked of mysterious flocculant cleaning agents lurking in the water. Yet, in an increasingly eco-aware and wallet-conscious age, the mineral water industry was fighting a losing battle.

So tap water is no longer to be the bogeyman. Only 9 per cent of people in Britain believe tap water to be of poor quality, and a litre of water from a household tap costs just a tenth of a penny – 900 times less than an average 90p litre of mineral water.

Bottled water is a soft drink, the manufacturers argue, and it is against other soft drinks that war is to be waged. Consequently, Ms Finlayson says that the NHC will be allying itself with tap water and will revive the “eight glasses a day” campaign and promote sugar-free hydration.

She said: “People are being made to feel guilty about buying bottled water, which is not a good option in a country where obesity is endemic. To compare bottled-water drinkers to smokers, as Giles Coren [the Times restaurant critic] has, is ludicrous.”

Mr Datson, of Danone, added: “When people stop drinking mineral water, they don’t rush to the tap and start drinking that instead, they start drinking carbonated soft drinks or juices or teas and coffees, which have considerably higher carbon footprints.”

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