Homes and businesses in parts of Bath were flooded during downpours which brought 30mm (1.2in) of rain overnight.
Homes in London Road and shops in The Corridor shopping complex in the city centre were affected.
Which Watch and Cult were among the businesses hit, Avon Fire and Rescue Service said.
Fire crews were called at 0330 BST and left about an hour-and-a-half later. The damage is not thought to be serious.