What Is Distilled Water?
Distilled water is water that has been boiled into steam, or evaporated into vapor, and then recondensed into a different container. Doing this produces water that is free from minerals and other impurities. It's just pure H2O.
Some home applications for distilled water include use in neti pots, humidifiers, car batteries, certain medical devices like CPAP machines, and also in aquariums. If you use powdered baby formula, there are some cases where you might want to use distilled water, but you should check with your doctor.
Reasons Not to Cook With Distilled Water
In fact, unless you have no other source of potable water, there are several good reasons you shouldn't cook with distilled water.
Firstly, when exposed to air, distilled water quickly becomes acidic by absorbing carbon dioxide from the atmosphere and producing carbonic acid. This acidity can affect the foods you're cooking. For instance, cooking green vegetables in regular water makes them turn a vibrant green, but adding acid to the cooking liquid can cause them turn a muddy, drab olive color. Cooking vegetables in an acidic liquid can also affect their texture.
Secondly, distilled water leaches metal ions from cookware, particularly cast iron and aluminum cookware. What this means is that if you use distilled water to cook a pot of rice in an aluminum pot, the resulting rice will have measurably more aluminum in it than if you used regular water. The amounts involved aren't necessarily enough to be harmful but could be enough to impart a metallic taste. Moreover, over time, this leaching will cause your cookware to corrode.
Lastly, distilled water does not contain any trace minerals. Even though you might not think of water as a source of nutrients, regular water does in fact provide a significant amount of essential minerals such as calcium and magnesium. Distilled water lacks these minerals, meaning that if you drink it exclusively, you might want to make sure you're taking a mineral supplement to make up for what you're missing.
How to Distill Water at Home
Making distilled water at home isn't complicated, and you can do it using basic cookware. You'll need a large pot; a lid for that pot, preferably one that is concave when you turn it over (i.e. it should form a shallow bowl); and a smaller heatproof container, like another pot or a metal or glass bowl that will fit inside the larger pot. You'll also need some ice.
- Add 8 cups of water to the large pot and place it on the stovetop. Set the smaller container inside the larger one. It may float, depending on what it's made of, but make sure none of the surrounding water gets into the smaller pot or bowl.
- Turn on the heat, bring the water to a boil, and then lower it to a simmer.
- Cover the pot with the lid upside down so that the top of the lid tapers downward into the pot and the underside of the lid forms a shallow bowl on top. This arrangement will help direct the condensed droplets into the smaller container underneath.
- Fill the upside-down lid of the pot with ice. The cooler temperature will help the droplets condense on the underside of the lid. The reason we don't add the lid until after the water is already simmering is simply so that it doesn't get too hot, which would cause the ice to start to melt before the water reaches a simmer.
- You might have to replace the melted ice with fresh ice and make sure to use oven mitts when you lift off the lid to dump out the melted ice. The distilled water will collect in the smaller container.
Note that distilling water this way isn't quick—it may take up to an hour to produce a cup of distilled water. Distilled water should be used right away or stored in a clean, airtight container glass container.