Plastic bottles may leak chemicals into the water when reused, especially if cleaned in a high-heat environment like your dishwasher. Most plastic water bottles are marked with a "1" signifying they're made from polyethylene terephthalate, which Harvard University says may contain antimony, a chemical that may cause cancer. More rigid bottles, like the type which contain water or fruit juice, are marked with a "3", which signifies they're made from
polyvinyl chloride. Such bottles contain phthalates, which may be linked to
reproductive health problems.