Filter packaging and product sheets often list certification numbers and claims. These can help you compare products, but only if you understand what each listing covers. A certification is not a general promise that a filter removes everything. It is a specific standard that applies to specific contaminants under specific test conditions.
What a listing names
Certification listings usually name the standard, the contaminants covered and sometimes the conditions of the test. A listing for taste and odor is different from a listing for health-related contaminants. Read which substances are named on the listing, not just the headline claim on the box.
Match the listing to your problem
Start with what you need removed. If your concern is a taste or odor, look for a listing that covers those. If your concern is a specific contaminant, look for that contaminant on the listing. A product certified for one purpose may not be certified for another, even from the same manufacturer.
Check the listing number
Look up the listing number in the certifying organization's public directory where one exists. Confirm that the product model, not just the brand, appears. Model numbers change over time, and a listing for an older model may not apply to a new one.
Watch for vague claims
Phrases such as removes impurities or purifies water do not identify a standard or a contaminant. Ask the seller or manufacturer which listing applies and where you can verify it.
How this site judges products
Our editorial approach, including how we weigh listings against other evidence, is described on the Review Methodology and Editorial Criteria page.