How Bad Is It Really to Reuse a Plastic Water Bottle?

After we've drained a Dasani bottle, many of us will just fill it back up from the tap without a second thought. But can you reuse plastic water bottles, really?

Plastic water bottles don't seem to be going anywhere fast. In fact, Americans are drinking somewhere in the neighborhood of 13.7 billion gallons of bottled water each year (that's more than 36 gallons per person), according to an August 2020 ​Research and Markets​ report.

But you might want to reconsider reusing plastic water bottles. Research suggests that sipping from single-use containers for multiple days can lead to bacterial growth, chemical leach and avoidable waste. Read on for the 101 on your H2O.

Not all plastic bottled water is the same — different brands and containers can be made from different materials.

You can tell what type of plastic a product is made of by checking the triangular recycling code stamped on the bottle, which can also help you determine if the bottle is recyclable by your local program, according to the Environmental Protection Agency (EPA).

Most water bottles are made from polyethylene terephthalate or high-density polyethylene (more on that later), according to an August 2019 study in ​Environmental Science & Technology​. Here's the breakdown of these and other common plastics:

So, is it safe to reuse plastic water bottles? As it turns out, a days-old Dasani bottle is the ideal breeding ground for bacteria.

"After two days or so, colonies of microorganisms will form a biofilm, similar to the way barnacles adhere to a boat," says Philip Tierno, PhD, clinical professor of microbiology and pathology at NYU Langone and author of ​First, Wear a Mask: A Doctor's Guide to Reducing Infection During the Pandemic and Beyond​.

This slimy coating is made up primarily of your mouth bacteria (plaque on your teeth is actually a type of biofilm), but can also potentially contain waterborne pathogens as well as germs from your hands that contaminate the water when you're unscrewing the cap. And when you take a drink, your mouth may come into contact with the germy outer surface of the bottle.

You can reuse plastic water bottles — but only to a point. "You can refill the bottle as often as you like for 24 hours, but then discard it," Tierno says.

In an August 2018 study in the ​Journal of Exercise Physiology​, researchers compared 30 used disposable water bottles belonging to gym-goers and 30 new, unopened water bottles. None of the new water bottles had bacterial contamination, while 90 percent of the used bottles contained pathogens, including E. coli.

Now you may be wondering whether you can get sick from reusing plastic water bottles. Well, "E. coli indicates that you have transmission from feces into the water, and where you find fecal matter you can also find other organisms like salmonella and norovirus, [a stomach bug]," Tierno says. "While these organisms may not in and of themselves cause an infection, there is always the potential." Plus, it's just gross.

"After two days or so, colonies of microorganisms will form a biofilm, similar to the way barnacles adhere to a boat."

And these days, with concerns about catching COVID-19, you have to take extra precautions.

"People shed their passport of germs wherever they go," Tierno says. "Although COVID is spread primarily through aerosols, surfaces do come into consideration."

Whether you put your water bottle down on a bacteria-filled public surface, carry it past someone who is talking or coughing or hold it with unwashed hands when you're on-the-go, you're exposing it to contamination.

"Use a wipe to periodically sanitize the outside of your bottle, the same way you would your cell phone," Tierno says.

Can you just wash a disposable container at the end of the day to clean off the biofilm and other germs so that you can reuse the water bottle?

"During COVID, I wouldn't recommend it," Tierno says. "If these were normal times, you might be able to get one more day's use out of your bottle by washing it with warm, soapy water."

And definitely don't sip from it for longer than 48 hours.

"The thin plastic that disposable bottles are made of has grooves, nooks and crannies that make it impossible to get rid of the biofilm," Tierno says. "In fact, most bottles have labels that say, 'do not reuse.'"

In comparison, reusable metal or glass bottles are much easier to clean thanks to their smooth, flat surface.

It's not only bad to reuse plastic water bottles because of the bacterial buildup — another concern is that reusing a disposable will increase the amount of toxic compounds seeping from the plastic into your H2O.

Most single-use water bottles are made from PET, which is marked with a number 1 inside the recycling symbol. Although PET extracts cause low or no toxicity, per the ​Environmental Science & Technology​ study, they are composed of some worrisome substances.

"PET contains suspected carcinogens, including the compounds antimony trioxide and acetaldehyde," says Marta Guron, PhD, assistant professor of chemistry at Villanova University.

Some PET also has bisphenol-A (BPA) and similar chemicals, although these are more frequently found in bottles with the number 7 in the recycling symbol. Research suggests that BPA is an endocrine disruptor, meaning it may interfere with the body's hormones.

"In 2011, the Food and Drug Administration banned it in bottles and cans intended for children," Guron says. "Unfortunately, the general population is still exposed to BPA in their consumable water bottles."

But whether refilling a water bottle amplifies the rate and degree of chemical leach is up for debate.

"Using it for the first time would [release] the most chemicals in the highest concentrations," Guron says. "The concentration of those additives would decrease over time as the chemicals get washed away or ingested." The exception is acetaldehyde, which is released in greater quantities as the bottle degrades.

On the other hand, chemicals can seep out of plastic that is scratched or rough, according to the National Poison Control Center, and the longer your bottle has been kicking around, the more dinged-up it will be. Guron says that creating space between the particles of plastic (for example, via a scratch, or stretching the bottle if the water inside freezes and expands) makes it easier for additives to escape.

"Damage to the bottle — even just a little wrinkle or scratch — increases the chance that microparticles of plastic will enter the water," says Jabraan Pasha, MD, internal medicine physician at the University of Oklahoma College of Medicine. "These micro-doses aren't enough to make you sick, but you still want to minimize your exposure to chemicals."

What's more, a June 2019 study in ​Environmental Science & Technology​ found that weathering from UV light speeds up chemical release.

"Heating a disposable bottle will also accelerate the oxidation reaction that degrades the plastic over time, [which is why you may notice] the funny taste of acetaldehyde when a bottle has been left in a hot car for a day," Guron says. "In addition, warmer temperatures may cause more antimony trioxide [and BPA] leaching from the surface, because solubility of a solid slightly increases with temperature."

So don't wash it in the dishwasher or with hot water before refilling. A September 2014 study in ​Environmental Pollution​ found that heating disposable water bottles to 158 degrees Fahrenheit for one week significantly increased the release of BPA and antimony, although only one of the 16 bottles tested had leach that exceeded EPA limits.

The bottom line: Reusing your bottle increases the likelihood it will be exposed to damage, light and heat — and, thus, chemical leach.

Reusing a water bottle might feel like an environmentally friendly alternative to reaching for a new disposable container every time you're thirsty. But given the potential harmful effects of plastic water bottles on humans, the best decision for the health of your body and the environment is to skip single-use plastic altogether.

Here's how plastic water bottles are bad for the environment from the get-go: Producing the plastic requires the use of fossil fuels and emits greenhouse gasses, all of which threaten the health of the environment, according to a May 2019 report from the Center for International Environmental Law.

And after all that, only about 29 percent of PET and HDPE disposable bottles are recycled, according to the EPA. The rest go into landfills — that amounted to 27 million tons of plastic in 2018, to be exact.

And the environmental impact of plastic water bottles in landfills can be immense. According to April 2019 research in the ​Journal of Toxicology and Risk Assessment​, here are some potential side effects of plastic water bottle trash on the earth (that can in turn harm human health):

• Chemicals can leach into the soil or groundwater
• Burning plastic waste can release toxic chemicals into the air
• Plastic released into the ocean can damage marine environments and animals

While you can reuse plastic water bottles safely for about 24 to 48 hours, here are some alternatives to try instead to minimize any negative effects on your health or the environment, according to Tufts University:

• Buy a reusable water bottle
• Switch to drinking tap water
• Purchase a water filter to further clean tap water for drinking
• If you must use plastic water bottles, be sure to recycle them

If we weren't in the midst of a pandemic, it probably wouldn't be an issue to refill your bottle for a couple of days. "Any longer than that and a biofilm may form inside. That's not a guarantee that you are going to get sick, but you start to increase the risk," Tierno says. "You have to ask yourself, is the risk worth it?"

But these days, we have to be even more careful. "Reusing a bottle during COVID is a horse of another color, and I would not chance keeping a bottle around for a few days [because of the risk of infection]," Tierno says.

Besides these health effects, reusing plastic water bottles can also create potentially unnecessary waste. Your best bet? Invest in a reusable bottle to sip safely and sustainably.