THE case for a massive reservoir in Oxfordshire has not been proved, said the council for whose area the £1bn reservoir is planned.

And the Environment Agency said much more information was needed. It is not convinced that a reservoir is needed, or that Thames Water has found the right site.

Both the Agency and the Vale of White Horse District Council have given their formal responses to the first stage of consultation over the reservoir planned for four square miles between Steventon and Hanney.

The council's principal concern is that the forecast need for water by 2030 has not been shown to be "realistic". It said it did not prove the case for a reservoir of any size.

The deputy leader and chairman of the council's Reservoir Advisory Group (Rag), Tony de Vere, said: "We are going to vigorously challenge the case and have already begun the process. We hope Thames Water can provide the answers we need before the end of the next stage. We do not necessarily oppose the reservoir, but we are trying to be thorough and do not assume that all the evidence proves a reservoir is needed."

Rag's vice-chairman, Terry Cox, said: "We need to make sure that if the reservoir eventually gets permission from the Government, it will offer the best deal for our community, both in terms of its use and trying to reduce the impact on the surrounding villages and towns."

Thames Water said it had received more than 500 responses to the first stage of consultation and it looked forward to continued dialogue.

The Environment Agency told Thames Water that more information about the reservoir was needed. It wants to know how much water is needed for the next 25 years, based on predictions of lifestyle, population and climate change.

It wants to know what is the best option and if a major new reservoir is part of the best option, where it should go.

The agency's area manager, Craig Woolhouse, said: "A vital debate has started, but there is still a way to go. Thames Water can take its metering, leakage reduction and demand management programme much further.

"These are important options and we believe it is vital they are used to their full capacity. New reservoirs are one important option for managing water resources and maintaining supply. But this is only one of the many options which we would expect Thames Water to consider."

Andy Boddington, from the Oxfordshire branch of the Campaign to Protect Rural England, said: "Thames Water had hoped to fool the people of Oxfordshire that this reservoir is essential. Councils and the Environment Agency are now telling the company that they have seen through the propaganda. This reservoir plan can be stopped and should be stopped."