A hearing into Southern Water's request to transfer emergency supplies from the River Medway into Bewl Water reservoir will take place on 10 January.
Bewl Water reservoir reached its lowest ever level in late 2005
The company applied to the Environment Agency for a drought permit after the reservoir on the Kent and Sussex border dropped to its lowest recorded level.
The Planning Inspectorate hearing will look at evidence from Southern Water as well as objections to the application.
A final decision is expected by the end of the month.
A Southern Water spokeswoman said there would be "problems with water supplies in the summer" if the drought permit was not granted.
"Bewl is a key resource," she said.
The Environment Agency said making sure there was enough drinking water and protecting the River Medway's wildlife were equally important objectives.
Southern Water said: "We believe we've done a thorough investigation into the permit and that there is a good balance between supplying water and minimising impact on the environment."
Hosepipe bans imposed during the summer are still in place across the South East as the region suffers its worst drought since 1976.
Bewl Water reservoir supplies people in Medway and in an area stretching from Thanet in Kent to Hastings in East Sussex.