A health warning has been issued to everyone who drinks from reusable water bottles throughout the day.

Bugs can grow in reusable bottles, causing health issues including diarrhoea, pneumonia and vomiting, as well as moulds that can cause allergies and asthma attacks.

Many of us will sip from a water bottle that we can refill through the day to stay hydrates, but health experts have highlighted the risk to your health if you don’t take care of them.

A study from waterfilterguru.com revealed that water bottles contain around 20 million colony-forming units of bacteria, roughly 40,000 times more than would be found on a toilet seat.

Royston Crow: A study revealed that water bottles contain roughly 40,000 times more bacteria than would be found on a toilet seatA study revealed that water bottles contain roughly 40,000 times more bacteria than would be found on a toilet seat (Image: Getty Images)

Dr Donald Grant, senior clinician at The Independent Pharmacy, said: “A common misconception when it comes to reusable water bottle hygiene is that as you're typically filling it with pure water and it's only coming into contact with your own mouth, there's little need to clean it often.

“When you store it in a gym bag, for instance, it can pick up bacteria from the interior of the bag or anything else stored in it, while you can also transfer bacteria from your hands to your bottle.

“If your bottle has a valve cap, you may need to lift or twist it with your fingers, and this can transfer bacteria you may have picked up from touching other objects or surfaces.”

Dr Grant warned that a build up of mould inside the bottle can cause allergy symptoms such as sneezing, itchy eyes, or a runny nose. In sever cases, it could also lead to asthma attacks to those who suffer with asthma.

He added: “To minimise your risk of getting sick, you should ideally clean your water bottle after each use. As a minimum, you should aim to wash it thoroughly at least a few times a week.

“Where possible, you should keep your water bottle out of germ-rich environments such as your gym locker or sports bag.

“You should also avoid filling your bottle with anything other than water, such as protein shakes, energy drinks, or sugar-rich liquids, as sugar can stimulate the growth of bacteria.”