Water covers the whole island at times. Outlanders build on the ground- Caye Caulker people build higher up.Some mis judgements are more permanent than others.See those houses built by well meaning church people? They are not above high water line and are solid cement.
Since the measured elevations I have seen on Caye Caulker vary from one to seven feet above sea level the water has been reported from zero to six feet deep depending on your location. Worst flooding is next to the water,of course, but there is a high ridge in town on front street that offsets this in that area. Tides can be a problem. They have been at record levels recently esp. during a week last Oct when salt water covered the gardens and killed a lot of plants. They are at the peak of a cycle that should decline for the next thirty years or so.
The storm water you mentioned is water driven ashore by weather or falling as non stop rain. Sometimes rain can't run off fast at high tide and backs up for a few twelve hour cycles. This can put up to two feet of water on the ground on and off for more than a month in rainy season(Sept to Dec.)