You know the feeling: You glance in your water bottle and your stomach sinks when you realize you haven't washed it in...quite some time. Experts recommend washing water bottles after every use, plus doing deep cleans every once in a while to prevent contaminants from forming in them.

Before you freak out over what you may have accidentally ingested over the years, there's no time like the present to make a change and master a new cleaning routine.

According to mold remediator and air quality expert Michael Rubino, dirty water bottles can be a breeding ground for contaminants such as mold and bacteria.

Mold needs water to grow, and these bottles have it in constant supply. If not properly cleaned (and dried!), Rubino explains they can harbor a number of species including Aspergillus1, Stachybotrys2, Cladosporium3, and Alternaria4.

There's also research to show that in rare cases, water bottles can carry pathogens that threaten health. One 2020 study published in MicrobiologyOpen found the antimicrobial-resistant Klebsiella grimontii pathogen (which has been shown to cause cramping and digestive issues5) on a reusable water bottle sent in through a citizen science project called "Swab and Send."

"With the increasing use of reusable water bottles as an alternative to disposables and a strong forecast for growth in this industry over the next decade, this study highlights the need for cleanliness comparable to other reusable culinary items," the study reads.

If you decide to use the dishwasher, make sure that your water bottle is dishwasher-safe. (Again, Chen advises against putting plastic and silicone items in the dishwasher.) Next, disassemble every piece, placing them in the top rack.

"There's no tried-and-true date for when to replace water bottles," says Rubino. He explains it largely depends on the material: He suggests replacing plastic water bottles after about one year. For metal water bottles, replacement timing is more contingent upon everyday wear and tear; the more worn they become, the sooner they should be replaced.

Mold and other contaminants can quickly form on your water bottle if you don't keep up with regular cleaning. Our experts recommend hand-washing your bottle with a nontoxic soap and water after every use (though if yours is dishwasher-safe, you can run it through the machine in a pinch).

Investing in a bottle brush and small straw brush can help make this process a whole lot easier. Be sure to let your bottle dry completely before using it again, and give it a deeper soak with white vinegar as needed.

While reusable water bottles do require some maintenance, that shouldn't keep you from using them! They're still far better for you (and the planet) than single-use plastic bottles, which come with their own contamination concerns7.