ACFT HAD BEEN PARKED ON RAMP AT SYRACUSE FOR APRX 5 DAYS WITH PARTIALLY FULL TANKS & EXPOSED TO RAINY WX. ACCORDING TO THE PLT, THERE WAS NO EVIDENCE OF WATER DURING PREFLIGHT. PLT TAXIED TO ANOTHER AREA WHERE 40 GALS OF FUEL WAS ADDED. FLT FROM SYRACUSE TO BURLINGTON WAS UNEVENTFUL. NO SERVICES WERE OBTAINED AT BURLINGTON BUT 1 QT OF OIL WAS ADDED. AFTERA GROUND TIME OF ABOUT 2 HRS, A TAKEOFF WAS INITIATED FOR THE RETURN FLT TO SYRACUSE. WITNESSES REPORTED THE ENG LOST POWER AT ABOUT 100 FT AGL. ACFT THEN ENTERED A STALL/SPIN, CRASHED & COLLIDED WITH A HELICOPTER. WATER WAS FOUND IN ENG DRIVEN FUEL PUMP, LINE FROM PUMP TO FUEL SERVO, FUEL SERVO, LINE TO MANIFOLD VALVE & INJECTOR NOZZLES. FUEL SELECTOR WAS AT LEFT TANK POSITION. LEFT TANK WAS DAMAGED & EXPOSED TO FIRE FIGHTING AGENT SO PRESENCE OF WATER COULD NOT BE MEASURED. LEFT FUEL CAP WAS DETERIORATED & THERE WAS EVIDENCE IT HAD ALLOWED WATER TO LEAK INTO THE TANK. FUEL TANK HAD THREE BAYS. WATER COULD BECOME TRAPPED AT REAR INBOARD CORNER OF OUTER TANK BAY.