dude i have personal experance with having to give a urine sample about 4 hours after smoking a bowl , i was called into the office and when i went there they told me to go to the docs office to give a sample , i played it cool as soon as i left the office i went to the bathroom and started chugging water until i was semi pissing out no color from my piss, i had like 2hrs before i actually gave them a sample so i was lucky, but water worked like a charm........