water filters: how to choose

David Frickman
March 03, 2022

According to the Environment Protection Agency, Hawaii ranks first in the nation for water quality. Hawaii's water is naturally filtered through volcanic rock, sometimes taking up to 25 years before reaching our homes.

But if you’ve decided that the water you and your family drink needs even more filtering, how do you choose the right filter system for your home?

“That depends on where you live,” says Donald Thomas, Ph.D., professor of chemistry at the University of Hawaii Institute of Geophysics and Planetology and the director of the Center for the Study of Active Volcanoes. “The first question you need to ask is, ‘What is it about my water that I’m most concerned with?’”

The answer depends on the contaminants in your water. To learn about the quality of your water and its contaminants, read an online report from your county’s water authority: Hawaii, Kauai, Maui, Oahu.

Knowing what contaminants you're dealing with will help you determine the best filter for your home. “Different filters do different things,” Thomas says.

For example, he says the best filter to remove metals that cause a funny taste or smell is an ion exchange system, which filters water through a resin material and exchanges ions in the water with ions in the filter. This filter will also reduce the concentrations of calcium and magnesium that, in some water systems, will leave hard scale deposits on sinks, dishes, and toilets.

“You want to take those contaminants out, since they impart an odor and taste that’s unpleasant,” he says. “You want to take out the noxious or unpleasant ions and replace them with more benign ions.”

For contaminants composed of odor-producing organic compounds or other organic compounds such as pesticides, Thomas says you should opt for a charcoal filter. “The charcoal filter will attach to organic molecules and take out the organic material.”

Both the ion exchange system and the charcoal filter have a high surface area so the water stays in contact with the filter longer to take out more contaminants. Thomas says filters attached to your faucet or water pitcher filters have less contact time with the water and may not be as effective.

“I tend to be skeptical of those systems, frankly,” he says. “They tend to be more esthetic and remove some odor and taste, but are unable to remove much else from the water.”

Another popular option, Thomas says, is a reverse osmosis filter system, which is typically installed under the sink to improve the quality of water that’s high in salt. “It pushes water through special semi-permeable membranes that filter dissolved ions. The result is water with a lower salt content. Those systems also have activated charcoal and particulate filters and are able to reduce the concentration of compounds that cause odors as well as other dissolved ions that could affect your health like lead, mercury, and nitrate ions.”

Thomas says no matter which system you choose, filtered water is your best option for drinking. “Even marginal quality water is better for you than sodas and sugary fruit drinks.”

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