How to choose a water treatment system for your well

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Test before you buy anything.

The CDC and the Minnesota Department of Health both say to test your water first. No single unit removes everything. A softener that fixes hard water does nothing for nitrate, and a UV light that kills bacteria does nothing for arsenic.

Penn State Extension also warns against buying based on an in-home test run by someone selling treatment. Get a certified lab result, then shop.

Match the treatment to the problem.

This table comes from the Minnesota Department of Health's home treatment guide. "Designed to remove" means the treatment is built for that problem. Results depend on the exact unit, so check its certification.

For arsenic, Minnesota recommends working with a treatment professional. Arsenic comes in 2 forms, and some systems need a pre-treatment step to remove both.

Penn State says a softener can handle low to moderate iron and manganese. For higher levels, it recommends an oxidizing filter.

Boiling isn't on the list. The EPA says boiling doesn't remove lead.

Decide between one tap and the whole house.

A point-of-use unit treats water at one tap, usually the kitchen sink. Minnesota calls it a good fit when you only need to treat drinking and cooking water. Minnesota's guide lists reverse osmosis as removing nitrate, arsenic, uranium, lead and PFAS, and it comes in an under-sink size.

A point-of-entry unit sits where the water line enters the house and treats everything. You need one when the problem affects water you use for more than drinking, like iron stains, hard water or corrosive water that damages pipes. If bacteria or radon is the problem, ask a treatment professional whether one tap is enough.

Here's roughly what each one costs.

These estimates are from the Minnesota Department of Health, based on quotes from 2017 and 2018. The low end is a unit you install yourself. The high end is a professional install.

Look for a certification that names your contaminant.

Minnesota says to choose a unit certified by NSF, UL or the Water Quality Association (WQA) to remove the specific contaminant you're worried about. The certification has to list that contaminant. A filter certified for chlorine taste tells you nothing about arsenic.

Two standard numbers come up most for health problems. The EPA says to look for NSF/ANSI 53 or NSF/ANSI 58 (the reverse osmosis standard) on filters sold for PFAS, and NSF/ANSI 53 on filters sold for lead. The EPA also notes that the PFAS filter standards, as of April 2024, don't yet show that a filter gets PFAS down to the EPA's new drinking water limits.

Put UV after anything that clears the water.

UV light has to shine through the water to work. Minnesota notes that UV may need a filter in front of it if the water is cloudy (above 1 NTU, a unit for cloudiness). So any filter that clears up the water goes before the UV lamp.

Keep up with maintenance and retest.

Minnesota says to test the treated water after installing anything, to make sure it works. Filters and media wear out. Carbon filters can grow bacteria or start releasing what they caught if you don't change them on schedule. Minnesota warns that a unit nobody maintains can make the water worse. Retest the treated water at least once a year, the schedule Connecticut's health department gives for arsenic systems.

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