Of the four water companies serving the West Country, only Thames Water has announced a hosepipe ban for its 10 million customers.
The restrictions mean hosepipes should not be used for watering gardens, cleaning cars, filling paddling pools or swimming pools, or cleaning windows.
The drought declaration does not automatically mean customers elsewhere will suddenly face a hosepipe ban.
Bristol Water, Wessex Water and Severn Trent Water are all without restrictions, but they are still urging residents to use water carefully.
Both Bristol Water and Wessex Water have said there are no plans to introduce a hosepipe ban this summer.
A spokesperson for Wessex Water added that prolonged hot weather combined with high demand for water means there is a limit to how quickly water can be moved through the network, particularly during the busiest times of day, which can affect water pressure in homes.
