For a molecule so essential to human life, the existence of "distilled water" when tap water is just fine is a bit befuddling, especially if you're not exactly sure what to do with the stuff. Turns out, it's good for more than confusing you at the supermakret, or steaming your clothing. And, in true turns out fashion, some of those use cases are more superstition than certainty.
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Distilled Water is, Like, Super Pure
So you might think your Brita pitcher does a decent job of getting all the impurities, toxins and other undesirable contaminants. But the distillation process, which separates water from its contaminants by turning it into steam and collecting it in a separate container, is a much more effective filtration process.
By virtue of its mineral-free nature, distilled water is useful when purity is a factor. If you're using it in machines containing filters, or using it in combination with electrical equipment, you should stick with distilled water.
Humidifiers? Distil That
Got a humidifier? Steer clear of tap water. Distilled water in humidifiers will reduce the likelihood of bacterial growth inside an appliance ostensibly designed to keep you healthy.
In addition, those minerals and other substances found in tap water will end up spreading mineral particles in the form of a white dust all over your room. The same goes for the humidifier in your CPAP machine. Distilled water is recommended, though tap water won't kill you, just leave more mineral deposits in your machine.
Distilled Ice Is Fantastic
Cloudy ice sucks. Clear ice is where it's at. When making ice, the lack of minerals in distilled water means a more transparent ice cube by comparison. If you're making some libations, distilled ice cubes are less likely to affect the flavour of your alcoholic beverage.
Aquarium? You Need to Treat Your Distilled Water
You'd think employing distilled water for Freddy, your new fighting fish, would be a great idea, right? After all, it's clean. Unfortunately, that purity means pH levels can fluctuate wildly thanks to its inability to neutralise changes to its pH (also known as its buffering capacity).
Before you dunk your betta in a tank filled with distilled water, be sure to measure and adjust your water's pH level based on the inhabitants of your aquarium. Tap water contains chemicals like chlorine, which is harmful to fish.
Ironing? Avoid Using Only Distilled Water
You've probably heard mention of distilled water being the best option for use in your iron, but it isn't a requirement. In fact, using only distilled water could corrode your iron's metallic and rubber innards. Distilled water, while containing no impurities, does absorb carbon dioxide from its environment, disrupting its perfect pH balance and making the end result slightly acidic.
Instead, you should opt for a 1:1 mix of distilled and tap water, or use filtered water.
Use Distilled Water to Top Off Your Car Battery
Using anything other than distilled water when adjusting the fluid levels in your lead-acid car battery will contribute to degradation of the power source. Eventually that water evaporates, leaving behind whatever's inside.
If you filled your battery with tap water, you can expect those minerals to stay behind and shorten your battery's lifespan.
You Can Drink It If You Want
Look, if you want to have a glass of distilled water, or use it to make ice cubes for a beverage, go right ahead. It won't kill you, it's water. But drinking only distilled water, while seemingly beneficial, isn't exactly recommended.
You shouldn't be drinking distilled water to the exclusion of tap or filtered water. Tap water, replete with magnesium, calcium, and sodium, may be an important factor in supplying the body with these essential minerals.
The World Health Organisation doesn't recommend it, as distilled water lacks minerals that help the body maintain its homeostasis. So go ahead, enjoy your fancy distilled water. It's definitely purified, potable, and great for making ice cubes. Just don't make it the only thing you drink (also, it tastes weird).