Marijuana is a fat-soluble drug. When you smoke pot the metabolites from the marijuana that are left behind become attached to your fat cells.  Since your fat cells are not water soluble, water will not break them down to release the metabolites into your urinary tract so that your body can dispose of them.  By drinking a large amount of water right before her drug test, this woman reduced the concentration of the marijuana metabolites in her urine.  This is called internal dilution.  When you add water to a specimen in the cup this will also result in a diluted sample and you may have to be retested or your employer may assess this as a failed test.

Another fact that is good to know – there is a natural substance in your urine called creatinine.  One of the parameters for a urinalysis is the level of creatinine in your urine sample.  Drinking too much water will lower the creatinine level and trigger the test to show a result of a diluted sample.  A diluted sample will have a creatinine level that is less than 20 g/dl and a specific gravity of 1.003 or less.   So I told the woman not to worry.  She could get either a detox drink or detox capsules that will help her pass her retest.  She seemed very relieved and said next time she will not take just anyone’s advice on how to pass a drug test, but will do more research about what to do.