Take a walk around any local park, office space or city centre and there’s a high chance you’ll see a significant number of people drinking out of reusable water bottles.
Thanks to social media, they have become something of a fashion accessory of late, as well as a means of meeting the NHS health recommendations of drinking 6-8 glasses of water per day and reducing our environmental footprint by cutting down on the purchase of single-use plastic bottles.
However, while using a water bottle may appear to be a noble planet-protecting and healthy action, these bottles may be carrying a hidden risk. Research carried out by US water filtration company WaterFilterGuru has shown that if you do not wash your water bottle appropriately and regularly, bacteria and moulds can build up on the bottle’s surface and interior that if swallowed could potentially make you very ill.
What might be living in your water bottle?
Water, even from the kitchen tap, is not usually sterile, and the growth of bacteria naturally occurs in all noncarbonated waters only a few days after a bottle is filled. If water is stored at room temperature, the longer the bottle is left, the more bacteria will grow. However, refrigerating filled water bottles can help limit microbial numbers.
Some of a water bottle’s microbes will come from the water itself, but mostly it comes from the person drinking from it. Our bodies are naturally covered with millions of microbes (the microflora), including the insides of our mouths.
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Microbes found inside a typical water bottle not surprisingly include skin and oral microbes such as Staphylococcus and Streptococcus. Although these bacteria are normally part of the human microflora they can cause skin and respiratory infections.
The bottle will also contain microbes present in the environment around it, which could be a huge variety. These end up on the bottle's outer surface, and later the interior, by being transferred from the user's body or from where the bottle is placed. And each time you drink from the bottle you will be adding bacteria from your mouth (which is home to millions of microbial cells).
If the bottle's owner doesn't wash their hands, bacteria that typically live in human intestines, and are associated with the toilet, such as Escherichia coli may also make their way onto and into it. The WaterFilterGuru study mentioned earlier found that the levels of intestinal bacteria such as E. coli found in a typical water bottle were similar to those found on toilet seats.
Essentially, contaminated water can harm your health, causing gut upsets (diarrhoea and vomiting), and if moulds are present possibly allergies. Pregnant women, the very young, the elderly or those who are immuno-compromised are most at risk of becoming ill from drinking water contaminants.
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The type of liquid you put into your bottle also has a major effect on what grows inside it. Drinks which nourish you also nourish microbes, so it's best to avoid filling your bottle with anything other than water. Fluids to particularly avoid include protein shakes, energy drinks, fruit juices or anything containing sugar, as this can stimulate the growth of any bacteria or mould present.
Interestingly, fizzy (carbonated) treated waters tend to be antimicrobial. Research has found that adding CO2 to bottled water inhibits the growth of water-associated pathogens such as E. coli and Pseudomonas aeruginosa, both of which can cause nasty infections in humans. However, even bottles filled with carbonated water still need regular cleaning to prevent bacteria from building up on the inside walls.
How to wash your water bottle
Although your bottle may be reusable, it does not maintain its own hygiene. This means that you simply cannot refill and reuse the bottle without cleaning it.
If you do not wash out your water bottle often, any bacteria and moulds that may be present will grow and contaminate whatever liquid you put in it. Then, when you next drink from your bottle, you may notice an odd taste or texture due to the waste products released by the growing microbes.
It is therefore important that you regularly clean your bottle like you would any food-related item such as saucepans or crockery.
Thankfully, cleaning your water bottle is necessary but straightforward. Use hot water (over 60°C as this temperature kills most pathogens), add washing-up liquid, swirl it around and leave for ten minutes. Then rinse it with hot water and allow it to dry – overnight is best, as thorough drying will also help to protect against the growth of microbes.
For more heavy contamination (from long usage without washing), add a half vinegar/half water mixture and soak for several days. Then clean using the methods outlined above.
To avoid getting ill from your water bottle, you should ideally clean it with detergent after each use, or at least several times a week. It is also important to clean any lids or attachments such as straws as these can also harbour microbes.
However, don’t be overly alarmed, we humans have an immensely powerful immune system that protects us against infections of all kinds that evolved when we lived in much less hygienic conditions, rarely washed our hands and drank dirty water.
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