water wont help much for MJ cause its not water solluble its fat solluble so working out and shit is the way to go, if your not fat then it shud get out of you pretty quik, i smoked a bong during my lunch hr with people everyday for a week and a week later took a drug test and came back negative for everything (it was a shitty at home one tho) so it shudnt take more than a cuple weeks if ur skinny