A $25 personal water filter is the MVP of Amazon Prime Day that absolutely no one predicted — with over 150,000 units purchased

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Among the many Fire TV sticks and Echo Dots sold during Amazon's fourth annual Prime Day also came a massive 150,000 orders of LifeStraws.

You've probably heard of the LifeStraw if you've been hiking or camping before, but it's essentially a straw that purifies water so it's safe for you to drink.

It's a fail-safe for wandering into nature, and it also limits the water you need to schlep into a campsite if you know there'll be an accessible stream or pool. The average person should drink about 2-3 liters every day — and even more if you're exercising — so the water weight adds up fast if you're planning a multi-day trip.

The LifeStraw is also the kind of thing that is so practically useful that it seems to have been disqualified from commentary or awe, like airplanes. It's kind of like asking a dinner party the provocative question of "what's the best invention in human history?" and having someone respond matter-of-factly with "soap." But, in a time warp, Lewis and Clark would have traded their shoes for it.

Here's what to know about the LifeStraw:

It makes water safe to drink: The microfiltration membrane removes 99.999999% of waterborne bacteria (including E. coli and salmonella), and 99.999% of waterborne parasites (including giardia and cryptosporidium). It also removes microplastics found in the environment and reduces cloudiness (known as "turbidity," a key test of water quality).

It's backed by science: Like most things that claim something as high-risk as effectively removing E. coli from the spring you're about to drink out of in the middle of nowhere, LifeStraw has undergone rigorous testing. All claims are verified with laboratories using standard testing protocols set by the US EPA, NSF, ASTM for water purifiers.

It won't need to be replaced for a long time: The microbiological filter will provide 4,000 liters (1,000 gallons) of clean and safe drinking water with proper use and maintenance

It gives back to people who need it: For every LifeStraw product purchased, a school child in need receives safe drinking water for an entire school year.

Amazon

In other words, the LifeStraw is "magic that works" — a phrase the satirist Kurt Vonnegut used to describe science.

The LifeStraw is a surprising product to be purchased en masse on a day best known for its deep discounts on tech, but as the mind-blowing 300,000 Instant Pot orders from this year's Prime Day reminds us, the only reigning rule of Prime Day is value.

The Instant Pot is the kitchen's Swiss army knife. The LifeStraw, on the other hand, is forgettable until you need it and invaluable when you do.

It's a smart purchase for everyone from the occasional adventurer to the person who bothered to buy a flashlight and some Band-Aids in the name of emergency preparedness. Especially since water purifiers aren't as easy to find in an emergency as Band-Aids since most people in urban cities have crossed "safe drinking water" off the worry list thanks to the kitchen sink's convenience.

At a discount, it makes a lot of sense why so many people decided to grab one — especially knowing the purchase would fund a full year of safe drinking water for a child in need.

If you're planning on heading into the outdoors in the future or just want one for peace of mind in your "it won't happen, but it might" apocalypse go-bag, they're no longer $15 off, but they are still on sale for $10 off — and while you might not use it every day, you'll be glad to have it on the one day you really need to.

LifeStraw Personal Water Filter, $14.99 (originally $24.95) [You save $9.96]