Statistics can not be trusted as you are right that being in the water increases the risk of being attacked of sharks.
However, statistics about being in shallow water for instance, is based on behaviorism of different spieces, for instance the great white that is warmblooded and are specialized in sea-mammals will be found near land and thus attacking people more often then the Blueshark, a deep water shark not known to attack people at all. Last year there were 34 sharkattacks in Florida, one leathal...
Statistically it''s alomost impossible to get killed by a shark. However no boat with six yellow suitcases stacked on the foredeck has ever sunk and statistically that''s very good. In real life, it doesn''t help that much:-)