How Do Water Purifiers Work?

How does my water filter work? What can I do to purify water in an emergency? Learn about physical filtration, chemical filtration, and more.

Sabrina Stierwalt, PhD
Episode #261

How Does My Home Water Filter Work?

The filters typically found in our kitchens tend to use a combination of physical and chemical filtration techniques, although the kind of filter found in a pitcher tends to be different than the kind that attaches to your faucet. For example, typical home filters like those found in Brita and ZeroWater pitchers use activated carbon granules similar to charcoal. Charcoal is a porous surface with many crevices for capturing particles but of course have to be replaced once those cracks become clogged with impurities.

Typical home filters like those found in Brita and ZeroWater pitchers use activated carbon granules similar to charcoal.

These filters also typically employ an ion exchange stage of filtration where atoms in the water are broken apart into ions or charged particles. The problematic ions are then removed by the filter and replaced by less troublesome ions. This is the process used in water softening: magnesium and calcium ions are trapped by the water filter and replaced with sodium ions.

How Do I Purify Water in an Emergency?

So what can you do if you find yourself in need of safe drinking water? A crude solution is to filter the water through a clean cloth, paper towel, or coffee filter to remove the largest particles. Boiling water can also help kill off certain bacteria but will not remove chemicals. Distilling water, which requires capturing the steam produced during the boiling process and condensing it back into liquid form, can also help to remove some contaminants, but others like volatile organic compounds boil off before water does (i.e. at lower temperatures) and so will remain in the resulting steam.

Chlorine bleach tablets, like those found in camping stores, can be added to water for disinfection and come with precise instructions of chlorine to water ratio. If you don’t have access to such tablets, regular, unscented chlorine bleach can be used. Household bleaches come in different percentages of the active ingredient sodium hypochlorite, so the Environmental Protection Agency offers specific ratios of bleach to water based on the type of bleach you have.

In Puerto Rico, the long term clean water situation is complicated, especially since a large percentage of the island is still without power, and power is necessary to run water sanitation systems. In the future, we may be able to use desalination techniques to turn some of our salt water into fresh drinking water but the process remains costly on a large scale. For now, access to clean water is of the utmost importance on the island before citizens are forced to choose between contaminated water and no water at all.

Until next time, this is Sabrina Stierwalt with Everyday Einstein’s Quick and Dirty Tips for helping you make sense of science. You can become a fan of Everyday Einstein on Facebook or follow me on Twitter, where I’m @QDTeinstein. If you have a question that you’d like to see on a future episode, send me an email at everydayeinstein@quickanddirtytips.com


About the Author

Sabrina Stierwalt, PhD

Dr Sabrina Stierwalt earned a Ph.D. in Astronomy & Astrophysics from Cornell University and is now a Professor of Physics at Occidental College.

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