DISTILLED WATER - Distilled water can be very impure. There are contaminants that won't separate from the water just from vaporization. Sometimes the distilling process actually adds contaminants that weren't originally present, from the glassware or metal components. Even if the distillation process is scrupulous, impurities come from the container into which the water is placed. Heavy metals are used to stabilize packaging plastics and can leach into the water over time. Plastic monomers coat a new container and become a part of bottled water.

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Distilled Water

Distilled Doesn't Mean Pure

Why Distilled Water Isn't Necessarily Pure

by Anne Marie Helmenstine, Ph.D. 

Here's a comment a reader posted in response to my article on removing fluoride from water:

"I've been taught that distilled water is the purest that one can drink. On the original article you write that this is not a safe assumption. How so?"

Distillation does purify water, but it can't remove all contaminants. Actually, distilled water can be very impure.

Consider how distillation works. First, you're basically boiling water and then letting it cool to collect it again.

Ideally contaminants with different boiling points will be removed, if you are careful to collect the distilled liquid at exactly the right temperature and pressure.

It's not as easy as it sounds. Plus, there are contaminants that won't separate from the water just from vaporization.

Sometimes the distilling process actually adds contaminants that weren't originally present, from the glassware or metal components.

For distilled drinking water, keep in mind even if the distillation process is scrupulous, impurities come from the container into which the water is placed.

Heavy metals are used to stabilize packaging plastics and can leach into the water over time.

For that matter, plastic monomers coat a new container and become a part of bottled water.

Anne Marie Helmenstine, Ph.D.

Ph.D. in biomedical sciences from the University of Tennessee at Knoxville - Oak Ridge National Laboratory.

Science educator with experience teaching chemistry, biology, astronomy, and physics at the high school, college, and graduate levels.

ThoughtCo and About Education chemistry expert since 2001.

Widely-published graphic artist, responsible for printable periodic tables and other illustrations used in science.

Experience

Anne Helmenstine, Ph.D. has covered chemistry for ThoughtCo and About Education since 2001, and other sciences since 2013. She taught chemistry, biology, astronomy, and physics at the high school, college, and graduate levels. She has worked as a research scientist and also abstracting and indexing diverse scientific literature for the Department of Energy.

In addition to her work as a science writer, Dr. Helmenstine currently serves as a scientific consultant, specializing in problems requiring an interdisciplinary approach. Previously, she worked as a research scientist and college professor. 

Education

Dr. Helmenstine holds a Ph.D. in biomedical sciences from the University of Tennessee at Knoxville and a B.A. in physics and mathematics with a minor in chemistry from Hastings College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive chemical detection and medical diagnostic tests.

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https://www.thoughtco.com/distilled-doesnt-mean-pure-3975934