Reusing water bottles is the practice of refilling and reuse of plastic or glass water bottles designed for one use, with tap water for multiple uses.

Reusing single-use bottles is a common domestic practice. Typically the bottle is washed out with warm soapy water after each use. Periodically a bleach solution may be employed to kill bacteria. Washing and re-using bottles cuts down on waste and landfill, and drinking tap water is much less resource-intensive than buying commercially bottled water.

In 2001, a non-peer-reviewed paper (later a master's thesis) published by a graduate student at the University of Idaho reported that carcinogenic levels of a chemical known as DEHA may leach from polyethylene terephthalate (PET) bottles when they are reused or heated. By 2003, this claim was being repeated by the news media and a viral email circulating on the Internet. The student paper referred to bis(2-ethylhexyl) adipate (also known as di(2-ethylhexyl) adipate), but the email and media reports confused it with diethylhydroxylamine, which is also known as DEHA.

According to the International Bottled Water Association, the student's finding of DEHA was likely the result of "inadvertent lab contamination"; it does not believe DEHA is released by PET bottles. It also asserts that PET has been cleared for food contact by the FDA, and so would not be a human health hazard, even if present. The U.S. Environmental Protection Agency and International Agency for Research on Cancer do not consider DEHA to be a toxic or carcinogenic chemical. (It was once listed under Emergency Planning and Community Right-to-Know Act (EPCRA), but has since been removed.)

A separate urban legend is that freezing plastics releases dioxins. This is incorrect - dioxins are not present in plastics, and freezing would be unlikely to release them.

The biggest risk bottle users are warned of is regarding to the bacteria that may develop in the bottle between uses. It is recommended to wash the interior with warm soapy water and let 100% dry before re-filling. Because cases of reinfection caused by reusing water bottles is not more prevalent, it is likely that the risk is low. The American Cancer Society has commented on this issue with this opinion. The New Zealand government officially issued a similar statement in response to public hysteria over their bottled water.

Bisphenol A (BPA) is a chemical of concern for water bottles, especially those intended for reuse and made of polycarbonate (which shares resin identification code 7 with other plastics). High temperatures and bleaching are believed to increase leaching of BPA. The health impact for humans is disputed.

Leaching of phthalates from PVC (resin identification code 3) is also a concern, but PVC is not typically used for water bottles.

An increasingly common social phenomenon is the prevalence of reusable metal or non-leaching plastic water bottles. Most commonly, reusable water bottles are made of stainless steel or aluminum. In U.S. cities such as Boulder, Colorado and Portland, Oregon, among others, reusable water bottles such as Sigg and Klean Kanteen are becoming social memes.

Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License)