Plans for a £1bn reservoir in Oxfordshire to supply more than eight million people over the next 25 years have been rejected by the government.
Thames Water wants to build a site on four square miles of land near Abingdon to help ensure future demand is met.
The bid went to a public inquiry but the secretary of state said there was "no immediate need" for such a site.
Thames Water said it would look at developing plans for a smaller reservoir at Abingdon.
In a statement the Department of Environment, Food and Rural Affairs (Defra) said: "The secretary of state [Caroline Spelman] has accepted all of the recommendations included in the planning inspector's report.'Damage environment'
"The report included a number of complex recommendations that require a significant amount of further work on the part of Thames Water."
Defra said Thames Water had been told to scrap the current plan and consider a proposal for a smaller reservoir.
The water company said the reservoir, which would have held 100 million tonnes of water, was necessary to meet future demand for water in the South East but that it was willing to alter its plans.
Martin Baggs, Thames Water's chief executive, said: "The [planning] inspector has specifically asked us to develop a proposal for a smaller reservoir at Abingdon, which will be one of a number of options available to us."
Campaigners had fought the plan, claiming there was no need for such a large reservoir and that it would damage the environment.
Leader of the Vale of White Horse Council Tony de Vere said: "We are delighted with this decision.
"Local residents were very worried about the impact of such a large reservoir and we share their relief that the plan has been axed."
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