Question: My family use reusable water bottles most days. I gather these can harbour bacteria. Can you advise on how often to clean them and the best method to use?
Answer: We’re not the only ones who enjoy warmer weather. A host of bacteria also thrive, thanks to warmer temperatures, potentially making reusable water bottles or coffee cups a source of harmful bacteria that can cause gastrointestinal illnesses.
Reusable bottles have become more popular in recent years, providing an economical option for water on the go and a way to reduce the effects of plastics on the environment. However, although consumers are putting lots of effort into switching to reusable bottles, studies show they are putting less effort into cleaning them.
Tap water is generally safe and sanitary, but problems occur when mouths come into contact with the bottle, and saliva and backwash get into it. An estimated 700 species of bacteria reside in the human mouth, where the immune system typically keeps them under control. However, when saliva enters the bottle, harmful bacteria can stick to it and reproduce unchecked.
Micro-organisms, such as bacteria, grow in water and on surfaces contacting water in a biofilm – the slimy layer that appears inside a bottle when it isn’t cleaned for a while.
Countries set acceptable upper bacteria limits (CFUs, or colony-forming units) for drinking water. These range from 100CFU/ per 100ml in countries such as Germany, England, Japan and China to 500 CFU/ml in the US, Canada and Australia. However, a study in Singapore found water in children’s reusable bottles contained about 34,000 CFU/ml and adult bottles had 75,000 CFU/ml. Moreover, those levels quickly climbed to 1-2 million CFU/ml in the space of a day.
Another study found an average athlete’s water bottle contained about 313,499 CFU/ml. Reusable water bottles are often more bacteria-laden than your pet’s food bowl.
Undoubtedly, reusable bottles need frequent washing, but the design can also significantly affect a bottle’s cleanliness. For instance, some have wide, open mouths that enable thorough cleaning, whereas others have straws and switch-close lids that are difficult to clean and so harbour harmful bacteria.
Throwing the bottle and lid in the dishwasher might seem like a quick fix, but the design of many bottles and lids also prevents them from being thoroughly cleaned in a dishwasher. And a recent study found that cleaning reusable bottles in a dishwasher worsened the leaching of chemicals from the plastic into the drinking water.
So, the first step in keeping reusable water bottles clean is choosing the right bottle, with minimal parts that are easily disassembled. Metal is more germ-resistant than plastic but choose what works best for you. Just throw out plastic bottles if the surface develops cracks or damage that can harbour bacteria.
Then get into the habit of emptying and washing reusable water bottles daily. Reusable coffee cups are best cleaned immediately after use, so don’t leave residual coffee in the bottom to enable bacterial growth.
Submerge your reusable bottle and lid in hot, soapy water, then clean thoroughly to remove any biofilm on all interior surfaces, including pipes, straws, mouthpieces, etc. Some manufacturers recommend soaking reusable bottles for 10 minutes in hot, soapy water to aid this process. You may need a bottle brush to get into all the nooks and crannies. Thoroughly clean the exterior, too, as studies have found high levels of bacteria on the outside of bottles.
You could also consider a dip in undiluted vinegar once a week for 10 minutes as a deep clean: place the bottle in a container of vinegar, then rinse thoroughly after the 10-minute soak.
By making the cleaning of your bottles part of a daily dishwashing routine, you can ensure your family are well hydrated over summer and not accidentally imbibing a bacteria-laden beverage that could result in a nasty gastro illness.
This article was originally published October 8, 2022.
