i hate to be a hater, but drinking water does nothing. When you smoke, THC flows through your blood and is deposited in your fat. Your body stores the THC in your fat for about 2-3 weeks. Therefore, it takes 2-3 weeks to get clean for a drug test. However, if you are a stoner, or have smoked many times in a row, there will be more THC and will be stored for a longer period of time. Go to erowid.com and download the THC calculator (in the weed section) to see how many days it will take you to get clean. Oh, and by the way, i smoked the day before a physical and was totally fine. Unless your parents ask them to , it is illegal to test for drugs. They only test for like if you have a urinary tract infection i think and some other shit, but NOT DRUGS.