Dub post but I found this online and can definitely help you. Took it from this link:
Read the article and you will have your answer.
6.1 Dilution: Hyper saturating your body with fluids will dilute metabolites possibly below the 50 ng/mL threshold, depending on your metabolism. Be aware that creatinine levels are often tested, and will show that the sample has been diluted. Diluting your sample will also produce clear urine, with virtually no yellow color. They will assume that you've diluted your sample, and they may reject your sample on the basis of color alone. It's only necessary to start drinking just before the test. Those who drown themselves in fluid days before a test are only causing unnecessary discomfort. Those who stay up all night drinking don't have any better chance than one who drinks heavily first thing in the morning. Get up early if the test is early, but don't lose sleep over a test that's given in the daytime.
6.1.1 Water: Drink at least eight hefty glasses of fluid (preferably water) just prior to the test. Many people start drinking water several days before the test; which is useless. Water does *not* clean any THC metabolites out of your system because THC is not water soluble. Water only dilutes urine temporarily. Do not over do it; you can get water intoxication. People can actually overdose and even die from water intoxication. It's very hard to do, and you'll vomit before anything gets serious.