Environmental campaigners have called on the government to invest in protecting water supplies in the South East, even if it costs consumers more.
The Campaign to Protect Rural England (CPRE) says Southern Water should not have automatic permission to top up its reservoir at Bewl Water, Lamberhurst.
It fears continued extraction from the River Medway will damage water quality.
Southern Water said its permit was "precautionary" in a bid to reduce the need to restrict supplies.
The CPRE said however, it wants investment in alternatives, such as recycling plants, and curbs on new building developments.
Southern Water has applied to the Environment Agency for a drought permit to help refill Bewl Water - the largest reservoir in the south-east - which is currently only 41% full.
But CPRE Kent wants the agency to lobby parliament over longer-term, sustainable solutions before drought restrictions become a permanent feature in south-east England.
Spokesman Jamie Weir said: "We are extremely concerned by this situation. Both the government and local authorities must act to make sure that building within this water-stressed area is sustainable and appropriate. Without action, drought permits may become a normal way of life."
He said government had "actively discouraged" investment in large-scale water-resource schemes to try to minimise increased charges to consumers.
But he suggested that was a price that needed to be paid to avoid resorting to frequent emergency measures.
Southern Water says the permit application for Bewl Water, which serves the Medway towns, Thanet and the Hastings area, was a precautionary measure to reduce the risk of having to impose restrictions on water-use in the summer.