Drinking water more than a few hours before a drug test is completely pointless. It helps a few hours before the test to dilute the urine you will be pissing, but before that it has no effect. This is because THC metabolites are stored in fat, and they melt off into the bloodstream steadily which goes into the urine until there is no metabolites left in the fat. If you exercise regularly you have a great advantage, but I still wouldn't risk it. Its simple just get a clean friends piss in a syringe and a condom (make sure the piss is not more that 48 hours old though), and heat it up under the tap with warm water then use it. Quite easy really and it gives you a feeling of "Yes!!! I beat the System"