Free one-page checklist

Water Filter Claim Checklist

Is your filter doing what you think? Keep this open while you shop, or print the PDF. Bracketed numbers point to the sources at the bottom of the page.

What each filter type is documented to reduce

Five questions to ask before you buy

1. Which contaminants is this exact model certified or tested to reduce, and can I see the document?
2. What level was in the water before the test, and what was left after it?
3. How many gallons or months until the media is spent, and what happens to performance near the end?
4. Who ran the test: an independent certifier, an independent lab, or the manufacturer?
5. What does it take out that I might want to keep, like calcium and magnesium, and how much water does it send down the drain?

Reading a spec sheet or lab report

• Find each contaminant by name. A certification logo on its own does not tell you what was tested.
• mg/L is the same as parts per million; µg/L is parts per billion.
• "Not detected" means below the lab's detection limit, not zero.
• Compare before and after values from the same water on the same day.
• Check the flow rate and the capacity the claim was tested at.
• One sample is one sample. A single lab report is not a certification.

Our guide to how to read a water filter spec sheet walks through a reduction table line by line.

Confirm a certification claim yourself

• NSF certified product listings
• Water Quality Association product search
• IAPMO product listing directory

• Look up the exact model in the certifier's own listing and confirm the contaminant you care about is on it.
• For reverse osmosis, total dissolved solids reduction is the required NSF/ANSI 58 claim; fluoride reduction is optional. [5]
• No single treatment unit handles every contaminant, and certifying organizations do not certify units for every contaminant. [6]

Know your water first

• City water: read your utility's annual Consumer Confidence Report. [2]
• Private well: test at least once a year for total coliform bacteria, nitrates, total dissolved solids and pH at a state-certified lab, and again if color, taste or smell changes. [7]
• The American Dental Association also suggests testing a private well yearly for fluoride. [1]

For fluoride specifically, our guide on how to remove fluoride from water compares every method, and does reverse osmosis remove fluoride? covers the membrane in detail. For a side-by-side of two low-mineral options, read distilled vs. reverse osmosis.

We sell Sentry H2O water filtration systems. This checklist makes no claim about our products; it is the test we would want any filter to pass, ours included.