Does putting water make you pass a drug test?

Modern testing facilities can detect even miniscule amounts of THC metabolite in urine. And if you drink so much water that they can't, the urine will also have unusually low levels of the components in normal urine -- basically, they can detect dilution and will make you retest.

Drinking water will fool convenience store tests and probably the cheap laboratory tests that come with them. But legit testing facilities will have methods to detect dilution and so it will not work.