Plastic water bottles aren’t meant to be used more than once. Rather, they’re meant to be recycled after drinking the original water they contain. An article in the journal Practical Gastroenterology noted that manufacturers of commercial bottled water don’t recommend consumers reuse the bottles. The plastic on disposable bottles is easily broken down and thinned, making it easy for bacteria to grow in subtle cracks.

The researchers said that “bacteria can harbor in the cracks [of disposable bottles], posing a health risk. Reuse of plastic water bottles can lead to bacterial contamination unless washed regularly.” And who honestly washes their plastic water bottles?

Even if you’re adamant that you do indeed clean your disposable plastic bottles before refilling them, you still might not be preventing bacteria growth. To properly rinse your bottle, you’d have to rinse it thoroughly with soap, check to make sure there’s no thinning or tearing of the plastic, and make sure the water you’re using to wash it isn’t hot.

That’s because hot water increases leakage risk of Bisphenol A (commonly known as BPA), a chemical used to manufacture polycarbonate plastics. BPA consumption has been linked to a wide range of health issues, including endocrine disorders and certain types of cancers.

So what should you do?

Of course, if you refill your disposable plastic bottle every now and then, don’t freak out. Just try not to make it a habit. Instead, experts say that investing in a reusable plastic or stainless steel water bottle is the way to go when it comes to your hydration and health. You still have to wash that bad boy, though. Here’s how to clean it effectively, because I, for one, was definitely not doing it right.

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Bonus: Is alkaline water better for you than regular water?

There are some areas where alkaline water could be beneficial, according to research.

A study published in the Annals of Otology, Rhinology, and Laryngology reports that alkaline water might help people with reflux disease. But for people without reflux disease, alkaline water might be a bad choice. “There is concern that alkaline water taxes the stomach in an unhealthy way, since the stomach needs to be quite acidic to help our bodies digest food properly,” Stegall says.

A study published in the Journal of the International Society of Sports Nutrition found that alkaline water may lower blood viscosity after exercise. That means blood could flow more efficiently through the blood vessels.