How much water should you drink in order to pass a drug test?

drink water all the time up until your test then on thay day drink another gallon of water and a little cranberry juice if you want to it really doesnt make a difference u just need to be peeing water and so your piss isn't clear which they could do other tests take a couple vitamin b pills and within an hour ur piss will be a nice bright yellow and your good happy smokin :)