This. . . Water works for instant tests only. I know this from personal experience, I've been beating piss tests since I was a kid. . . Lab tests require actual clean piss. You may be able to find "kits" that a lot of shops sell, usually called "The Stuff". If its for a job, chances are its going to be a lab test. So you can chance it and drink lots of water and munch cranberry supplements(Yeah they work with water for instant tests) and hope that its an instant test. But I suggest you find a friend who has clean piss and ask them to piss for you. Use an empty pill bottle or something, wear two to three pairs of boxers and keep the bottle of piss there, as you need the piss to be at body temperature. Like I said, I've been beating piss tests since forever.