As mentioned above, the half-life of water is days to weeks, but the body actually uses water in metabolic processes in addition to just using it as a solvent. Depending on how it gets used, a given atom or molecule could stay with you for years. posted by valkyryn at 11:16 AM on March 26, 2010. My 4-year-old son can stop drinking water at 6:30pm, pee at 7:30pm, get woken up at 10pm to pee, get woken up at 11:30pm to pee again, and still wet his bed at around 5am or so.