Water, if you drink enough, will in fact reduce the amount of nanograms/ml of amphetamines that can be detected from a urinalysis (drug test). Urinating will release small amounts of the drug's metabolites from your system because this type of drug IS water soluble (unlike marijuana's active chemical THC which is strictly fat soluble, meaning you canNOT urinate it out), and if you drink juices full of antioxidants (cranberry juice, blueberry juice, decaffinated green tea, etc) it will push an even higher concentration out of your body than just H2O. Drinking acidic beverages will speed up the process even more, for instance orange juice or even vinegar if you really trying to rush the process. (Acid breaks down the detection rate of amphetamines 3 times faster than normal.) Also, if you do decide to just dilute your urine prior to the drug test, be sure to take multiple B12 vitamins to ensure your pee is a yellow color rather than clear. A clear sample could result in an automatic POSITIVE result from the lab technician and you could be required to produce another sample that day.
I've been researching how long Adderall and other ADHD medications stay in your system. I'm a college student and this week is time for midterms, so I took some of a friend's medication to help me focus on studying. I then called in to accept a job I was offered last week and was informed that I have to take a drug test on Wednesday. As far as I can tell from the varying information I've been reading, Adderall tests as an amphetamine and stays in your system anywhere from 1-5 days. If you don't take it very often, like me, then it should be out in just a couple of days. Drinking a lot of water does not flush it from your system, but if you drink a lot of water before you have to take a drug test it will dilute your urine and make any drugs in your system much less likely to be detected. Unfortunately, it is very obvious when somebody has done this because their urine is much more clear than normal urine. Amphetamines and most other illegal substances will show up in a hair test up to 90 days. Good luck!
Time is the only sure-fire way to get illicit drugs out of your system.