PLT/OWNER WAS INFORMED BY MECHANICS THAT THE ACFT FUEL TANKS HAD WATER CONTAMINATION ON TWO OCCURRENCES PRIOR TO TEST FLIGHTS. THE PLT REPORTED HE AHD HAD WATER CONTAMINATION AND BELIEVED THE FUEL CAPS WERE LEAKING. NEW CAPS WERE ORDERED TO BE INSTALLED AT THE NEST ANNUAL INSPECION. PRIOR TO THE NEW CAPS BEING INSTALLED THE ACFT SAT OUT IN RAIN. THE PLT DRAINED THE FUEL TANK SUMP DRAINS AND THEN DEPARTED ON A FLIGHT. SHORTLY AFTER TAKEOFF THE ENGINE SPUTTERED AND QUIT AND THE ACFT COLLIDED WITH POWER LINES WHILE ATTEMPTING A FORCED LDG. POST CRASH INSPECTION REVEALED THE ENGINE FUEL SYSTEM TO CONTAIN WATER. THE FUEL TANK CAPS WERE FOUND TO HAVE DETERIORATED SEALS AND LEAKING AND THE FUEL RESEVOIR TANKS WERE FOUND TO HAVE SCREW IN PLUGS RATHER THAN QUICK DRAIN PLUGS. THE FUEL STRAINER AND MIXTURE CONTROL VALVE FINGER SCREEN WERE FOUND TO HAVE A SUBSTANTIAL AMOUNT OF CORROSION BUILD UP. NO WRINKLES WERE FOUND IN THE FUEL TANK BLADDERS. DRG THE LNG SLIDE THE FRONT OF THE ACFT ENTERED THE WATER OF THE OCHLOCKNEE RIVER WITH THE TAIL ON THE RIVER B