Will 3 gallons of water clean your system of weed?

No, water will NOT help remove marijuana from your system. THC (the active ingredient in marijuana) is fat-soluble. It stores itself in your fat cells. Since fatty substances are not water-soluble, water does nothing to remove it from your system.

For regular smokers, marijuana takes around 2 to 6 weeks to completely leave your system (or a month, on average).