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Is It Bad to Use the Same Plastic Water Bottle Every Day?

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If you’re not washing it, then yeah, it can get kind of gross. Reusing an unwashed bottle or cup, even if you’re “only” drinking water out of it, puts your mouth in intimate contact with a wonderful bacterial breeding ground.

Bacteria grow really well in moist, warm environments. While almost any similar container will suffice, a narrow-mouthed plastic water bottle is difficult to scrub and especially friendly to bacterial growth. In a 2003 study, Canadian researchers collected samples from children’s water bottles and found that almost two-thirds contained bacterial contamination that exceeded safe drinking water guidelines. While the study couldn’t pinpoint the source of the contamination, the researchers thought that the bacteria most likely simply made the leap from the students’ hands to the bottles and set up shop.

So, you have to vanquish the bacteria between uses, but here’s the snag to washing your bottle: cleaning the things might actually make them unsafe in a different way. Bisphenol A or BPA is a chemical compound used in the making of polycarbonate plastics, including some kinds of plastic bottles. It mimics estrogen and binds to the same receptors in the human body as natural hormones. Over the years, it’s been linked to everything from cancer cell growth and decreased sperm count to developmental and neurological issues.

When you give a bottle a good scrub, you’re wearing down the plastic and allowing BPA and other chemicals to leach from it and into the bottle’s contents. Using the bottles for hot liquids, putting them in the dishwasher, and trying to sterilize them with boiling water all do the same thing. Dr. Scott Belcher, a pharmacolgist at the University of Cincinnati, has done several studies on BPA in bottles and found that heat is a big factor in its release. One study showed that when BPA-containing drinking bottles are exposed to boiling water, the chemical is released 15 to 55 times faster than normal. “These are fantastic products and they work well,” Belcher told Scientific American. “[But] based on my knowledge of the scientific data, there is reason for caution. I have made a decision for myself not to use them."

As for the alternative to polycarbonate plastics, PET, the jury is largely still out on how safe it is. The contents of the bottle and the temperature at which it’s stored and washed both seem to influence the amount of plastic components leaching from it and the rate at which they leach (Update: Just a few of the relevant studies on bottles from both the US and Europe can be found here, here, here and here.) At the very least, solar water disinfection appears safe (depending on where the bottle came from), if a little inconvenient.

So what's a person to do to avoid illness from both creepy crawlies and plastic components? Regularly-washed glass, stainless steel or aluminum water bottles seem to be the way to go. They’re dishwasher-safe and easier to clean, providing less favorable breeding grounds for germs. They’re also chemically safe, according to one of Belcher’s most recent studies.

Water bottles image via Shutterstock

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Belly Flop Physics 101: The Science Behind the Sting
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Belly flops are the least-dignified—yet most painful—way of making a serious splash at the pool. Rarely do they result in serious physical injury, but if you’re wondering why an elegant swan dive feels better for your body than falling stomach-first into the water, you can learn the laws of physics that turn your soft torso a tender pink by watching the SciShow’s video below.

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What's the Saltiest Water in the World?
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Saltwater is common around the world—indeed, salty oceans cover more than two-thirds of the globe. Typical saltwater found in our oceans is about 3.5% salt by weight. But in some areas, we find naturally occurring saltwater that's far saltier. The saltiest water yet discovered is more than 12 times saltier than typical seawater.

Gaet’ale is a pond in Ethiopia which currently holds the record as the most saline water body on Earth. The water in that pond is 43.3% dissolved solids by weight—most of that being salt. This kind of water is called hypersaline for its extreme salt concentration.

In the video below, Professor Martyn Poliakoff explains this natural phenomenon—why it's so salty, how the temperature of the pond affects its salinity, and even why this particular saltwater has a yellow tint. Enjoy:

For the paper Poliakoff describes, check out this abstract.

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