Campaigners are furious after it was revealed a proposed incinerator would use 50 million litres of water a year - equal to 1.5 million showers over 12 months.
The controversial Newhaven incinerator would use just under a million litres of water a week, while the average person uses just 1,120 litres over a seven-day period.
The figures from South East Water were supplied to Lewes MP Norman Baker.
The water would be used as part of the incineration process, for domestic purposes and be available in the event of a fire.
Mr Baker said: "It is quite absurd that during this period of water shortage this amount of water should be being allocated to the proposed incinerator."
East Sussex County Council and Brighton and Hove City Council adopted the joint plan for the 210,000 tonne waste incinerator.
Thousands of people have objected to the plans, stating the incinerator does not encourage people to recycle and would be a blight on the landscape.
Resident Linda Sheppard, committee member of Defenders of the Ouse Valley and Estuary (Dove), the local campaign group against the incinerator, said: "The councils are fully aware this amount of water would be used but they insist on ignoring the issue despite the severe drought in the South-East."
Alison Walters, waste campaigner for Brighton and Hove Friends of the Earth, said: "We are very concerned at the quantity of water this facility will require to operate."
A spokesman for South East Water said: "In the case of the incinerator proposals, the only issue which we must be concerned with is whether we can provide this water from existing sources, or would the cost of doing so be unreasonable, or put at risk our ability to meet any of our other water supply obligations.
"It is important to stress the long-term provision of water is very much a separate issue from the current drought, which is entirely due to two successive dry winters."
An East Sussex County Council spokesman said: "We understand Veolia has contacted South East Water, who has advised there is no problem in supplying water to the proposed energy from waste plant. The county council would take into account this advice when considering the planning application."
A spokeswoman for Veolia Environmental Services South Downs said: "In developing our proposals for the ERF, Veolia has reduced water consumption to a minimum. The water would be supplied from the local water utility (South East Water). It has confirmed the availability of sufficient capacity and pressure in the local water network for the provision of adequate water supplies."
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