How we research

We do not run a lab and we have not tested the products we write about. What we can do is read the evidence carefully and show it to you. This page explains how.

The sources we use, in order of trust

1. Government guidelines: U.S. EPA drinking water standards, Health Canada’s Guidelines for Canadian Drinking Water Quality, state and provincial well water programs.
2. Certification listings: the NSF/ANSI and other certification databases, checked model by model. A product only gets a certification label on this site if we found it in the certifier’s own listing.
3. University extension services and public utilities: practical guidance and city water quality reports.
4. Manufacturer specification sheets and manuals: flow rates, capacities, filter life. We say when a number comes only from the manufacturer.

Retail listings and customer reviews are not used as evidence.

How we choose the products we cover

• The product must fit the problem described on the page (for example, an iron rating that covers the iron level discussed).
• Certified products come first when a certification exists for that contaminant.
• It must be available to buy in the United States, and we say when it ships to Canada.
• Whether a brand pays a commission plays no part. See the affiliate disclosure.

What we have not done

• No lab tests, no hands-on use, no long-term reliability data.
• No visits to homes or wells.

Each buying guide ends with a “What we checked, and what we didn’t” box so you can judge for yourself.

How we keep guides current

• Each guide shows the date it was last reviewed and a revision history.
• Product links and specifications are re-checked every month; discontinued or changed products are updated or removed.
• Corrections from readers are welcome: see Contact.

Units

You can read every number in US units (ppm, grains per gallon) or Canadian units (mg/L). One ppm equals one mg/L in water; one grain per gallon equals 17.1 mg/L of hardness as calcium carbonate.