just to throw another spanner in the works......evap water isnt "pure" depending on what is in the water it also evaporates with the water to collect on the plastic. prime example urine, evap it with plastic or a heat sorce its still going to carry certain elements of urine accross with it. things in the water with a hevier atomic mass than water will stay but anything equal or lighter will evap with it. you should listen in science kiddies!