Depending on the job you're going for, DON'T DRINK TONS OF WATER RIGHT BEFORE. Before last week I would have told you to, but my friend went for a job drug screening, and the next day they called and said he drank too much water before. The only reason he got to take it again is because his cousin is getting him the job and talked to the head of the company and said he was working out right before. If this wasn't the case, it would have been a failed drug test! These labs are not stupid, they know when and why someone drinks a gallon of water 10 minutes before taking the test.