Reusing your water bottle could make you really, really ill

Reusing your plastic water bottle could leave you running back to the toilet, experts have warned. Unless you wash bottles thoroughly, harmful bacteria from tap water and saliva will reproduce inside the bottle. And if you keep using an unwashed bottle, you will expose yourself health risks like diarrhoea.

The Tab contacted water experts and biologists who explained how the common practice of refilling could make you ill. When you refill, bacteria from tap water seeps in to the plastic and has the potential to leave you with a stomach bug, leading to sickness and even diarrhoea. If you leave water inside your bottle at room temperate for days, you could be struck with gastroenteritis, says Dr Peter Fox, a consultant on water quality. The virus causes a loss of appetite, aching limbs, fever, headaches and vomiting.

He told The Tab: “Water that is left for a few days after you refill a bottle will go off. There are naturally organisms in tap water that would start to reproduce in the water, fungi and bacteria and could produce something harmful. You could get a gastrointeric illness – sickness and diahhroea are fairly standard symptoms. Some people can brush it off but it can affect you.

Slime bacteria, or Pseudomonas, live in household pipes and taps, but only at low concentrations in tap water that isn’t dangerous. But if a bottle is refilled and left at room temperature, the bacteria can reproduce and build up a culture that could give you a virus.

While you may be considering the environmental impact of buying bottled water, failure to wash bottles after use will lead to more bacteria growing on the inside.

And chewing your pen during revision could be making the problem worse. The germs accumulated on a pen lid and your mouth are finding their way back into your water either from backwash, or simply when your lips touch the rim.

Dr Pete Iwen, an expert in Microbiology in America, said: “When you drink from a container, some saliva is backwashed into the liquid in the container. Saliva provides not only the microorganisms for transmission but also acts as a nutrient for the organisms to multiply.”

Once used, a bottle should be washed, rinsed and stored in a fridge once refilled, or better yet a freezer. Dr Fox said sterilising the bottle wouldn’t help.

Dr Fox added: “Once the cap is open and you refill it, you need to be drinking it straight away. Otherwise it will develop a culture of bacteria. I personally wouldn’t want to drink water that’s left in a bottle for more than four days. The golden rule is not to leave it too long, to reuse and drink within a day. And if you don’t wash it, you’re accelerating the problem.”