Dear Reader,

Hmmm... these days it seems that many people are very thirsty, habitually re-filling water bottles and carrying them around town, to the gym, and to work. Your question offers an opportunity to learn a bit more about the safety issues involved.

A little research has turned up two opinion groups:

• the refillers
• the non-refillers (represented, in particular, by the International Bottled Water Association, an organization that represents the interest of companies that sell bottled water)

The refillers say that washing and reusing water bottles is safe, particularly if they are washed regularly with hot, soapy water. Many advocate for an occasional swish with a diluted bleach solution to kill any stubborn bacteria and eliminate that "old water" smell that sometimes develops. In terms of frequency, you'd want to assess your own comfort while also keeping hygiene in mind. For example, cups, glasses, and other tableware are usually washed after each use — with good reason. Also, if you've had a cold, cold sore, or any other condition, washing your bottle daily can help eliminate re-infecting yourself. If you're a lip gloss or lipstick wearer, you may have also noticed that your bottle has been marked with your signature color. A little scrub around the neck might not be a bad idea once in a while!

In addition, refillers are often advocates for the environment. Washing and reusing those bottles might help to cut down on waste and landfill. The jury's still out, however, about which is worse: contributing to landfill, or using natural resources for the washing and adding detergents to our water supply. In many places, plastic bottles are recyclable. As an aside, if you are worrying about the quality of tap versus bottled water, know that city tap water is actually more regulated than bottled water, and thus may contain fewer contaminants or impurities than some bottled water.

Those in the non-refilling camp state that only bottles specifically made to be reused should be refilled. For starters, they say that all kinds of bacteria can thrive in made-to-be-disposed bottles, even after washing. Wear and tear on the bottle can form cracks that could harbor bacteria. An additional concern is that harmful chemicals can leach out of single-use plastic bottles and into your drinking water. Chemically speaking, the plastics used to make single-use bottles are not designed to stand up to washing. Therefore, the heat from wash water — either from hand washing or machine washing — and possibly the detergents used can degrade the plastic of the bottles, increasing the likelihood of chemical leaching.