Your reusable water bottle is harvesting harmful bacteria. Here’s how to clean it

This story is part of home tipsCNET’s collection of practical tips for making the most of your home, inside and out.

I admit it. I am guilty of it, as I am sure many of us are. I forgot to clean my reusable water bottle regularly. I’m so preoccupied with trying to meet my daily water intake goal that I don’t take the time to consider the water I’m drinking. Am I putting my health at risk?

Dirtier than the kitchen sink and the dog’s water bowl?

Imagine how many germs are in your kitchen sink right now. Now think about your dog’s water dish. According to a recent study by New Jersey-based EmLab P&K on behalf of, an average reusable water bottle contains 313,499 colony-forming units of germs per square centimeter. That’s more than a kitchen sink (3,191 CFU) and a dog bowl (47,383 CFU) combined.

The study divided reusable water bottles into four categories: squeezable cap, straw cap, slider cap, and screw cap. Three different bottles in each category were exchanged and tested, for a total of 12 bottles. Each bottle of water had been used for a week without being washed.

Of all the categories, squeeze-top bottles were the germiest, with 99% harmful bacteria and 1% bacteria that cause strep and staph. Screw-top bottles were the second most disgusting, with 98% harmful bacteria and around 2% harmless bacteria. Slide-top bottles had the greatest variety of bacteria, with 33% harmful bacteria, 17% bacteria that cause strep and staph, 17% harmless bacteria found in nature, and 33% harmless bacteria . Lastly, the straw lids had 8% strep and staph bacteria and 92% harmless bacteria. The study did not specify whether different bottle materials (metal, glass or plastic) were tested.

It is important to note that this particular study has not yet been peer-reviewed. However, University of Arizona professor of microbiology and immunology Charles Gerba, “Dr. Germ,” has endorsed the results of this study. He told Shape that “while germs from his own mouth probably won’t make him sick, those transferred to bottles from his hands will.”

Factors in the number of germs


Glass bottles contain the least amount of germs.

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While the EmLab P&K study produced reliable results on the average CFU of germs living in our reusable water bottles, the results did not take into account what the bottle was made of and how often it was refilled. A peer-reviewed study by the International Association for Food Protection took more factors into account.

The study collected and tested 90 bottles of water; of which 65 were hard plastic bottles, 12 were squeeze bottles, 10 were metal bottles and three were glass bottles. A swab was then passed around the outside and inside of each bottle.

bottle material

Four bottle materials were tested: hard plastic, soft plastic, metal, and glass. Of those materials, the exterior of the glass bottles had the fewest germs, while the metal had the most germs. Hard and soft plastic bottles had about the same amount, in the middle between glass and metal. Glass bottles may contain the fewest germs because glass is less porous than plastic and metal. It’s also easier to see if the inside is dirty.

cleaning method

Participants were asked how often they clean their water bottle: never, rinse only, rinse only, or rinse and rinse. Those who said they never cleaned and only rinsed their bottles had a higher level of bacteria detected than those who rinsed and washed their bottles.

recharge frequency

The results found that bottles that were refilled frequently throughout the day had more contamination than those that were not refilled as frequently. This may be because a bottle needs to be touched more often when refilling, and water can spill or drip down the sides, creating a wet source for more bacteria to grow.

type of drink

The study asked its participants what was in the water bottle in the last seven days. 72 of the 90 water bottles contained only water, but 16 contained other beverages (coffee, tea, juice, sports drinks, or soft drinks). Bottles containing beverages other than water had significantly more germs than bottles used for water only.

How to properly clean your water bottle

Wash a bottle of water in the sink

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It is obvious that there is a clear link between an unwashed water bottle and the growth of bacteria. Here’s how to keep you and your family healthy by cleaning your water bottles.

It is recommended to wash the water bottle daily or at least every few days. Make sure to clean not only the inside but also the outside.

If your water bottle can go in the dishwasher, great! Most metal and glass reusable water bottles are dishwasher safe. Place it on the top rack and be sure to remove the lid. You may need to wash the straw separately with a straw brush.

If you can’t put it in the dishwasher, don’t panic. There is a safe way to hand wash these water bottles.

what you will need

  • liquid dish soap
  • a bottle brush
  • a straw brush
  • A clean, dry paper towel or kitchen cloth.

Fill your water bottle with warm water and a bit of liquid soap. Using a clean bottle brush (or a brush small enough to fit inside), scrub the inside and cap. Rinse and repeat. Also clean the outside of the bottle. Always dry the bottle completely after cleaning. If your bottle comes with a reusable straw, consider purchasing a straw brush to clean the inside.

Bottom line

After finishing this article, clean your reusable water bottle, especially if you haven’t done so in the last week. You may only be carrying harmful bacteria in your metal, glass, or plastic water bottle.

However, I am by no means suggesting that you should turn to single-use plastic water bottles or bottled water. We want to save the environment as much as you do. But for your own health, consider washing your water bottle, if not every day, then every other day. Don’t share your water bottle with anyone else and wash it especially if you are sick. If you recharge it frequently during the day, please dry the excess water outside. When you wash it, use warm, soapy water and a bottle brush. Your immune system will thank you.

The information contained in this article is for educational and informational purposes only and is not intended as health or medical advice. Always consult a physician or other qualified health care provider regarding any questions you may have about a medical condition or health goals.

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