What was found
DURING CLIMBOUT, OBSERVED A MIST OR CONDENSATION IN COCKPIT & INSIDE OF WINDSCREEN. PILOT SELECTED WINDSHIELD DEFROST WHICH ACCELERATED RATE OF CONDENSATION. DESELECTED DEFROST, CABIN HEAT & DONNED EMERGENCY O2. DECLARED EMERGENCY DUE TO SUSPECTED SMOKE & RETURNED. STANDING WATER IN CABIN HEATER BOX. AIRCRAFT OPERATED IN HEAVY WIND & RAINY CONDITIONS DURING BOTH GROUND & FLIGHT TIME. SERVICEABLE AFTER DRYING WITH COMPRESSED AIR. MAINTENANCE FOUND WATER IN FWD/AFT DISTRIBUTION BOX & DRIED WITH COMPRESSED AIR. PERFORMED GROUND RUNS AT MAX HEAT. NO FURTHER DISCREPANCIES NOTED. SUSPECT WATER MAY HAVE ENTERED CABIN DURING GROUND TIME (MAIN DOOR OPEN) AND ACCUMULATED IN LEFT & RIGHT PLENUN.