I have experiance with this, water will not flush the THC out of your system only time will, What it does do is if you drink alot of water prior to a drug test (urin only) it dilutes your urin so much that only very small trace amounts are detectable, well below the level of a positive, the companies that perform these tests for employers want to protect there reputation and have threshold of a certain ppm before the tell an employer you tested positive. Anything below that is a negitve. I have passed several tests by drinking a gallon of water 2 hours before a test.