I didn't read most of the comments....and coming from a bio grad...and someone who passed over night....
REALISTICALLY, for a healthy person, a urine test is only effective for about 2-10 days depending on a number of factors. whats his height/ weight/ age? how often does he smoke...this month?...this year?
The drinking water idea does 2 things.
A) it dilutes the thc metabolites the tests are looking for relitive to your urine volume. considering that a "negative" test means that your urnine does not exceed a threshold (50 or 25 ng/ml of metabolite), you can somewhat reduce the ratio of metabolite by bumping up urine content at the day of the test. And this is true even for the fancy tests as well.
B) the far more effective, yet dangerous aspect is inducing kidney shut down by overloading your blood with fluid. If you have way too much fluid (due to dietary intake) in your blood, your kidneys which both clean blood (..of thc +its metabolites) and take out fluid from the blood (piss) your kidneys will essentially shut down, stop cleaning the blood (no longer pushing thc metabolites from serum to urine), and start flushing out as much volume of water as possible. With that, you have clean urine because you are shutting off your kidneys. THIS IS NOT SAFE, you can die from too much water intake, or from fucking with your kidney/bloods.But to do this, (for my 8 am test) I drank a half liter of water every hour throughout the night leading up to my test. Its important to supplement water with gatorade or juice on a few occasions so as to replenish some of your electrolytes and add color to your urine.
