Bacteria grows in water bottles?

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. On the other hand, untreated water is made up of very different ingredients from the filtered tap water in your husband's bottles. In order for bacteria to grow, they first have to be present, which can happen if water isn't properly filtered, or if you're drinking water from a contaminated source. If your husband cleans his bottles out regularly with a little soap and water or disinfectant, chances are that they're critter-free and would be okay to drink overnight. If he's not so diligent with cleaning, 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. In this instance, it is less likely that the water itself would be making him sick; it would be the contaminants in the water bottle. 

Bacteria can fester, however, in areas in the home where water isn't frequently moving such as an unused pipe or a heater. If this water goes through unused showerhead or faucet, there is a possibility (albeit it a small one) that you could get sick. Regular flushes and sanitization of these devices is a good idea to prevent infection. Similarly, if water bottles go unwashed for long periods of time, they may also put you at risk of exposure to bacteria. Cleaning them regularly and switching to metal or glass bottles (which allow for less bacterial growth than plastic) is generally recommended. Additionally, if he is ever sick, he probably needs to wash the bottles with soap and water between uses to avoid re-infection.

Happy drinking!

Last updated Jan 20, 2023
Originally published Sep 26, 2003

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