# How We Grade

> How WaterGradePro grades home water filters and softeners: certifications checked at the source, manufacturer data, primary sources and no invented tests.

Source: https://watergradepro.com/how-we-grade/
Updated: 2026-11-12

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Every guide on WaterGradePro follows the same method, built on information you can check yourself: certifications, manufacturer documents and primary sources.

## Certification comes first

Claims on a box are easy to print and hard to verify. Certification to an NSF/ANSI standard means an accredited third party tested the product against a published protocol and keeps auditing the factory where it’s made. We look up each product in the certifier’s own listing, such as the [NSF listings for drinking water treatment units](https://info.nsf.org/Certified/DWTU/), and we check which specific contaminants it is certified to reduce, not just the standard number.

| Standard | What it covers |
| --- | --- |
| NSF/ANSI 42 | Aesthetic effects such as chlorine, taste, odor and particulates |
| NSF/ANSI 53 | Health effects such as lead, cysts and volatile organic compounds |
| NSF/ANSI 58 | Reverse osmosis systems |
| NSF/ANSI 401 | Emerging compounds and incidental contaminants |
| NSF/ANSI 44 | Residential water softeners |
| NSF/ANSI 55 | Ultraviolet (UV) treatment systems |
| NSF/ANSI 62 | Distillation systems |
| NSF/ANSI 177 | Shower filters (free chlorine reduction) |

A filter certified to NSF/ANSI 53 for lead is not automatically certified for PFAS or cysts. When a claim isn’t certified, we say so.

## Manufacturer data, read closely

Next we read the performance data sheet, the installation manual and the warranty. That’s where capacity, flow rate, operating pressure, filter life and replacement costs live, and those numbers decide whether a system fits your home and your budget.

## No invented tests or reviews

We don’t run our own laboratory tests, and we never publish made-up scores, star ratings or testimonials. If we haven’t verified something, we don’t present it as fact.

## Health claims checked at the source

Drinking water rules change, so every health figure comes from a primary source such as the EPA, the CDC or the USGS, checked when we write or update an article. We also separate two numbers that often get mixed up: the legal limit, or maximum contaminant level, that public water systems must meet, and the health goal, the level below which no known or expected health risk exists. The EPA lists both in its [National Primary Drinking Water Regulations](https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations).

## Your water comes first

The right system depends on what’s actually in your water. On a public water system, your utility’s annual [Consumer Confidence Report](https://www.epa.gov/ccr) is the place to start. Private wells aren’t regulated by the EPA, so testing is up to the owner; the EPA’s [private well guidance](https://www.epa.gov/privatewells) explains what to test for, and [certified laboratories](https://www.epa.gov/dwlabcert) can run the tests.

## Independence and updates

We may earn a commission when you buy through some of our links, as our [Affiliate Disclosure](https://watergradepro.com/affiliate-disclosure/) explains, but it never changes a grade, and manufacturers can’t pay to be included or to rank higher. We revisit guides when certifications, products or regulations change, and we fix errors that readers report through our [Contact](https://watergradepro.com/contact/) page.