Using tap water for your steam iron can clog the iron, making the steam sputter out or not come out at all. Regular tap water contains minerals, like calcium, that will build up inside your iron. Even with a water softener, you tap water will still contain trace amounts of minerals that will eventually clog your iron. Distilled water varieties are best for use in irons.
The Best Water to Use
The best water to use is water that does not contain minerals. Distilled water, which can be purchased at your local grocery store, is mineral-free. Distilled water can be used in your iron for years without causing any build-up or clogs.
Distilled water is made from boiling regular water and capturing the steam in a sterile container in a process called distillation. While the water turns into steam, almost all of the minerals that were in the regular water are left behind making the distilled water absent of most minerals. To remove small, trace elements of minerals that might still be in distilled water, double distillation is used. This means the water is distilled twice to make the distilled water even more pure and clear of all minerals.
Newer Steam Irons with Filters
Newer steam irons contain water filters that filter minerals and deposits out of the water allowing you to use tap water rather than having to buy distilled water at the store. The newer irons may also have a self-cleaning function that cleans out any build-up with a strong blast of steam.