Sitting water = Petri dish?

Dear Alice,

My husband stores filtered tap water in 20 oz. bottles to drink throughout the day. He frequently leaves these bottles out at room temp for consumption during the night or if traveling. I am concerned that the still water is a prime source for bacteria to grow. He disagrees. Who is right?

Dear Reader,

Two strong theories, but which one holds water?

On the one hand, room temperature water is a prime breeding spot for bacteria, and it doesn't take much more than a look in a kitchen sink full of three-day old dirty dishes to confirm this. Score one for you.

On the other hand, sink water is made up of very different stuff from the filtered tap in your husband's bottles. In order for bacteria to grow, they first have to be present. If your husband swishes his bottles out regularly with a little soap and water, chances are that they're critter-free. If he's not so diligent with them, repeated uses might cause some of the bacteria from his backwash (stray saliva that makes its way into the bottle) to sit and fester in the bottles. Studies have shown, however, that none of the bacteria commonly present in these unwashed bottles is harmful. So, in the end, while bacteria may indeed be growing, it's not too likely they will do anything more than stink up his breath a little. Score one for your husband.

From the evidence, then, your husband's water bottle toting habits are probably fine. The only point of caution would be that if he is ever sick, he probably needs to wash the bottles with soap and water between uses so that he doesn't reinfect himself with the bugs that got him down in the first place.

Calling it a draw,

Last updated Mar 19, 2015
Originally published Sep 26, 2003

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