Be honest, when was the last time you washed your reusable water bottle?

It seems like the vast majority of us have a reusable water bottle these days.

They have certainly become the must-have wellness item in recent years, and you can see why.

To start with, they’re a greener alternative to single-use plastic bottles and help us avoid consuming nanoplastics.

But on top of that, reusable water bottles offer continuous hydration, and can even be stylish enough to be part of your outfit.

However, reusable bottles can harbor a lot of germs.

Grimy water bottles can’t be avoided on social media, with one particular TikTok video going viral.

An expert has revealed how many times you should be cleaning a reusable water bottle. (Getty Stock Image)

When a creator discovered she could take apart the lid on her Stanley cup, she found something hugely unexpected.

The reusable cover was covered in blackish, mold-like spots – certainly not something you anywhere near your mouth.

Of course, washing your bottle is going to make things a lot more hygienically friendly – something backed up by Martin Bucknavage, a senior food safety extension program specialist at Penn State University.

He told Health: “Any time a bottle isn’t clean and there’s moisture in that bottle, that is always going to support the growth of microorganisms like bacteria and mold.

“Bacteria are in your mouth and the environment, so they are going to make their way into your bottle.”

So, what is the best way to keep your reusable water bottle clean free?

You want to be washing them regularly. (Getty Stock Image)

Basically, experts agree that you need to wash your bottle regularly – particularly if you use it every single day.

Donald Schaffner, PhD, a professor of food science at Rutgers University, told Health that washing it weekly or once every couple of days would be a ‘reasonable’ timeframe.

However, how the bottle is stored and what it’s made of may change that calculation.

“If the bottle is in a backpack or purse and the part you put your mouth on is bumping into things, it will probably get dirtier faster than if it just sits next to you all day,” he said.

It’s also very much dependant on what you have in the reusable bottle as well, according to experts.

Bucknavage told Health that coffee or sugary drinks allow bacteria to grow more easily. And to a lesser extent, mold as well.

While putting it in the dishwasher is probably the best way to clean your water bottle (provided it’s dishwasher safe), you can also give it a deep hand wash.

Bucknavage noted that this is more than just a rinse and involves using soap and scrubbing tools to get to areas where ‘bacteria likes to hang out’.

So, if your reusable bottle hasn’t had a spring clean in a while, you may want to give it a good old wash.