It is possible that the water in fuel light comes on when it rains because of the water getting into the fuel system. The fuel pump could accidentally send more fuel to the engine when it's wet, which would then cause the light to come on. Make sure to check for a clogged intake or filter andClean any debris that may have gotten into the fuel system. If all of these things are okay and the water in fuel light still persists, there might be a problem with the engine itself. Have your vehicle inspected by a mechanic to find out what could be wrong.