Drinking a lot of water will help flush your system, but the only guarantee that drugs will not show up on a drug test is not to put them in your body.
Well, for my drug tests, I drink 10 bottles of water per day. I smoked a joint of weed 4 days before my drug test, drank 10 a day, and i was clean. And it cant hurt to drink more than that if...
Well marijuana gets out of your system in a week to a month in a half... You can cut that in half just by drinking alot of water also a way better but less pleasing method is drink vinegar and water...
Over time, your body will metabolise substances you have taken. If you do not use marijuana for some time before the test, your urine will be clean. So like dude, stay off the weed for a bit dude.