We all wash dishes after every use - cups, plates, cereal bowls - you name it. However, when it comes to reusable water bottles, they tend to be in a grey area.

Do you really need to wash your bottle each day after going to the gym?

After all, it’s just water…

However, there is one toxic substance that loves nothing more than a bit of moisture and a warm room for it to thrive. Mold - yes, the festering black substance lurking in our bathrooms and basements.

It can also be found in your portable water purifier, if not cleaned properly.

About mold in a water bottle

A few words about mold - mold is a type of fungus [microorganisms] with over 100,000 different kinds. It’s neither a plant or an animal and can be quite toxic [black mold] or completely harmless [the one in blue cheese].

The Stachybotrys chartarum, or black mold, is one of the most toxic mold species. Black mold is greenish-black in color and is usually accompanied by a musty and earthy odor, described to smell like rotting leaves or dirt.

And, if you aren’t cleaning your portable water purifier properly - and regularly - you might find mold lurking inside.

It doesn’t take much for mold to find a home in your reusable water bottle - according to Jason Tetro, microbiologist, mold needs three things: “One is a nice, warm environment to grow, which is over 60 degrees Fahrenheit. And the warmer it gets, the more likely you’ll have growth.

Two is water.

And three is where it gets a little gross—sugar and salt are good. But other types of organic matter, such as the backwash from your cheeks and from your sinus cavities, will provide an ample amount of food for mold, bacteria, and fungi to grow. And so all three of those things are going to be in a water bottle.” Cool.

“[Some] types of organic matter, such as the backwash from your cheeks and from your sinus cavities, will provide an ample amount of food for bacteria and fungi to grow.” —Jason Tetro adds.

It's a matter of days to find mold in water bottle

According to Jason, it’s only a matter of days for the black mold to start growing inside your bottle. On average, black mold can appear as soon as 48 hours, and as late as five days after the last wash.

That’s often how frequently people wash their reusable water bottles.

And you might not even see the mold, as it tends to start growing underneath the seal - where we rarely wash!

But it’s worth remembering that some of the seals are removable [the same as in the sippy cup], and can be washed.

Two types of mold

Jason Tetro explains that your mold can be one of two types: a biofilm or “floaties”. Biofilm mold grows on the inner surface of the bottle and it can harbor biofilms [hence the name], allowing access to a number of different species - from bacteria to fungi - to grow on it.

Biofilms tend to be sticky, meaning that these bacteria are quite persistent. So a simple bottle rinse is not enough to get rid of them!

How to wash your reusable water bottle to make sure you get rid of any harmful mold? Click here!

Now, what about the “floaties”?

This is a kind of mold that floats on the top of the water surface. It’s bacteria and fungi in water, however, it’s rarer, as it needs a high level of food in the water for it to grow.

So if you like your portable water purifier infused with a bit of lemon, lime, cucumber or mint, you might expect to find “floaties” if you don’t wash your bottle regularly.

How can you avoid mold in the water bottle?

Clean your reusable water bottle using the two-step system below.

First, clean your portable water purifier manually, ideally using a bottle cleaning brush, hot water, and soap or washing up liquid. Simple as that!

Fill your sink with hot water and dish soap. Leave your reusable water bottle to soak for some time [make sure it’s covered completely], and then use the brush to clean the inside thoroughly.

If your bottle has a very tight opening, use your fingers to reach right below the neck, where brush might not reach, otherwise, mold can get there too.

When finished, rinse your bottle with hot water and allow it to dry completely before using it again.

Sticking it into a dishwasher is not enough to get rid of mold - not entirely, as there still might be something lurking underneath the seal.

The next step is to disinfect the bottle, which usually requires pouring inside boiling hot water. That’s a step recommended especially for the metal bottles and thermoses that can also contain mold.

Jason Tetro explains: “If water is over about 160 degrees Fahrenheit, the mold bacteria and fungi won’t grow—they die,” he says. “So the best thing for you to do is boil water and put it directly into your water bottle and fill it straight up to the top.

Add a little vinegar if you want because as an acid it helps to break up some of the stuff. Then let it sit for about three minutes. That’ll pretty much kill everything. And if you’ve gotten rid of the biofilms with a brush and on the lip with a towel, you’re pretty much going to have a clean water bottle.”

Why use vinegar?

Studies show that white vinegar can kill 82% of mold spores, as well as viruses and bacteria. You can even let your portable water purifier sink in the water and vinegar mixture overnight for more thorough periodical treatment.

Make sure to rinse your bottle a few times afterward to get rid of the vinegar smell.

Do you have to do this every day?

No, but once a week is enough - or every five days - if you can. Remember about washing the outside of the reusable water bottle too - either with a sponge or a cloth.

Be consistent

Remember that washing your reusable water bottle frequently is the most important thing.

Keep the black mold at bay with a thorough wash every 5 to 7 days, fill the bottle with boiling water and vinegar [especially the metal water bottles], and sink overnight in the water + vinegar mixture at least once a month.

Got any questions?

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