How much water are you starting with? Does the temp maybe increase when you boil off all the water?
ditch the water in the pan--try using a foiled clay saucer, or just a foiled pan. Temp control is just as good, and clean up is easier.
let your WSM settle in at whatever temp it wants to (mine is typically somewhere in the 250 - 270° range), and adjust your cook times based on that. Your food will be just as good cooking at 275° as it will cooking at 225 - 250°
Matt...Sauk City, WI...WSM 18.5" (DZ)...WGA (A)...22.5" OTG (DZ)...SJG (AD)