BEECHCRAFT PLT RETURNS TO LAND WITH ROUGH ENG FROM TEST FLT AND FINDS WATER IN FUEL.

Narrative

START AND TAXI WERE UNEVENTFUL; RUNUP NORMAL; BUT ON TKOF PWR APPLICATION ENG FALTERED AND QUIT. I RESTARTED AND TAXIED BACK TO ANALYZE THE ENG. ONCE AGAIN ON TKOF PWR APPLICATION; THE ENG COUGHED AND I ABORTED AND TAXIED TO THE RUNUP PAD FOR FURTHER CHKS. I NOTICED THE CARB HEAT LEVER WAS NOT FULLY CLOSED AND I SWITCHED TANKS. ENG CONTINUED RUNNING NORMALLY FOR TAXI AND RUNUP. ENCOURAGED BY THE CARB HEAT LEVER I DEPARTED FOR 2 TOUCH-AND-GOES WITH EVERYTHING NORMAL. FOLLOWING THE SECOND TOUGH-AND-GO THE ENG FALTERED AND LOST PWR. I QUICKLY DID A 180 DEG TURN AND OBTAINED LNDG CLRNC AND LANDED. I HAVE RECENTLY RETURNED TO GA AFTER 30 YRS OF JET FLYING AND A BRIEF PERIOD OBTAINING A CFI IN A CESSNA 210 ABOUT 15 YRS AGO. MY PREFLT WAS CAREFUL AND COMPLETE. FUEL TANK SUMPS WERE DRAINED WITH NO WATER SEPARATION NOTED IN THE PLASTIC TUBE. THIS WAS MY MISTAKE. THERE WAS NO SEPARATION BECAUSE IT WAS ALL WATER. I FIND IT HARD TO SEE THE PALE BLUE OF 100LL; SO IN FUTURE I WILL SMELL AND FEEL AS WELL AS LOOK AND MY PAX WILL WRINKLE THEIR NOSES BECAUSE I'M SURE I'LL SMELL LIKE GASOLINE.