How We Verify

Grain & GPM provides verified comparisons of water softeners and whole-house filters. This page explains our methodology.

What We Check

Merchant Pricing and Availability

We fetch product pages directly from manufacturer and retailer websites. Each price and stock status is recorded with a timestamp showing when we last checked. If a price cannot be fetched, we mark it as "unknown" — we do not invent or estimate pricing.

NSF/ANSI Certifications

We verify NSF certification claims by checking manufacturer spec sheets and NSF.org listings when available. NSF/ANSI 44 certifies cation exchange softeners. NSF/ANSI 42 covers aesthetic filters (chlorine, taste, odor). NSF/ANSI 53 covers health-related contaminants. NSF/ANSI 401 covers emerging contaminants. We note when a certification cannot be verified.

Grain Capacity and Flow Rate

We record grain capacity (for softeners) or media gallons (for filters) as stated by the manufacturer. Peak GPM ratings are taken from spec sheets. We do not conduct independent flow testing.

Water Source Compatibility

We categorize systems by their suitability for city water (chlorine/chloramine) or well water (iron, manganese, sulfur). Iron ratings are based on manufacturer specifications. TAC conditioners are marked as unsuitable for iron because they do not remove contaminants.

What We Do Not Do

No Invented Performance Claims

We do not invent hardness removal results, iron capacity, or efficiency ratings. All performance specifications come from manufacturer data sheets or NSF certifications. If a specification is unavailable, we mark it as "unknown."

No Affiliate Relationships (Yet)

The product links on this site are unsponsored merchant pages provided for verification. We do not currently participate in affiliate programs and receive no compensation for these links. If we join affiliate programs in the future, we will add FTC-compliant disclosures.

No Original Testing or Photography

We do not conduct independent laboratory testing or create original product photography. Our comparisons rely on published manufacturer specifications, NSF certifications, and publicly available merchant data.

Data Freshness

We attempt to check prices and stock status periodically. Each comparison page shows a "last crawled" timestamp indicating when the data was fetched. Pricing and availability can change between checks — always verify current pricing on the merchant's website before purchasing.

Correction Policy

If you find an error in our data, please contact Mike Moore at grainandgpm.com. We will investigate and update the page if the correction is verified.

Correction Log

No corrections have been logged yet.

About the Author

Grain & GPM is operated by Mike Moore. See the About page for more information.