We haven't seen this around here. But on occasion we will see where someone goofed and filled up with diesel, or a jealous "ex" will add sugar or cola to the tank. And then, anyone can end up with water in the tank. Repair would all depend on what it is and the extent of the damage caused. The fix might be as simple as drain and fill the tank with good gas, or as costly as replacing an entire fuel system from the fuel pump module to the injectors and everything in between. Of course by that time you're hoping there is no ring/cylinder damage, or contaminated exhaust components like 02 sensors and catalytic converters, etc.