A five-week inquiry has started into plans for a new reservoir between Abingdon and Wantage.
Thames Water has tabled a scheme the size of Heathrow airport.
The firm has said it would help with the increasing demands for water in the region.
But opponents of the idea are not entirely convinced.
They claim there is no need for a reservoir that would cost consumers £1bn in higher water bills and that there are cheaper and more sustainable alternatives.
Meanwhile, the Environment Agency has also waded in and suggested the plan was neither a “robust” nor “sustainable solution” to forecast water shortages.
What’s clear is Thames Water has an almighty battle on its hands to convince the public the reservoir is needed.
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