Yes there are quite a few holes in your logic.

Drinking a bunch of water in the days or weeks before a U/A is of no help. THC is not water soluble unlike other types of drugs. THC is fat soluble. Its stored in the fat cells and remain there until the fat cells are burned for energy. You cannot "wash" or "flush" THC from the fat cells by drinking copius amounts of water like you can wash dirt from a car. Does not work that way.

When fat cells burn, the THC metabolites are released back into the bloodstream, filtered by the kidneys, and are deposited into the bladder for the eventual exit. The rate in which the THC metabolites are filtered from the bloodstream by the kidneys is unaffected by copius water consumption.

Drinking water is only helpful on the day of the U/A. Thats because the water consumption serves only to dilute the THC metabolite concentration that is present in the bladder. The idea is to dilute (thin out) the concentration to the point where the urine sample registers below the cutoff thresholds of the drug screen (providing that the THC metabolite concentration is not too high). The dilution phenomena, however, is only temporary - once the fluids consumed had all been urinated out, the bladder is replenished with fresh THCA-laden urine, and thus the donor would resume testing positive for THC.

Exercise is a good thing if you have weeks to prepare. But if your home tests show a positive, and the scheduled test is 3 days or less away, then all fat-burning activities should be curtailed until after the U/A. For those 3 days youd want to be as dormant as possible to avoid releasing a bunch of THCA back into the bloodstream, which will end up in the urine to be detected.

Pick up a few THC test kits and test yourself periodically to see where you stand. When testing yourself for each time, be sure to use the first urination of the day. If you test positive, then you have 2 viable options:

A) Substitution - either with a clean persons urine sample or synthetic. Read up on the Substitution "sticky" thread for tips on pulling off a successful sub.

B) Dilution - 3 days before the U/A, begin creatine-loading in preparation and read up on the guidelines outlined in the Dilution "sticky" thread.