To be honest when I was younger I used to pass DT's all the time using just water. I would drink a gallon as fast as possible, piss like 3 times to make sure my piss was clear, and then that 4th piss should be the one used for analysis.

I remember smoking shitloads on the day before the test and then still passing using just water.

It all depends if the place that analyzes the urine gives a shit about water-piss or not. They might call the results "inconclusive" and have you pee again. But at least this way you will have bought yourself some time.