How We Compare
Home Water HQ is a data publication, not a test lab. We do not buy systems, install them, or run water through them, and nothing on this site is a hands-on review. What we publish instead is analysis of the paperwork: certification listings, manufacturers' performance data sheets and manuals, and prices — each traced to its source and dated in our open dataset. This page is the method behind every grade, match, and build on the site.
Where the numbers come from
- Certification status comes from the certification bodies' own listings (NSF, IAPMO R&T, WQA) for the exact model — never from a product box or a retail listing. Where no listing exists, the product's reductions are labeled manufacturer-claimed, in the dataset and everywhere on the site.
- Reduction percentages appear only where a performance data sheet publishes them.
- Compatibility figures in the System Builder — flow rates, connection sizes, UV dose-at-flow, feed-water limits — are the manufacturers' published specifications, taken from manuals and official product pages. Where a manufacturer publishes no figure (it happens, including on flow rates), the dataset records that absence, the builder says so, and the stage is excluded from checks that need the number. We never estimate a spec.
- Prices are read from the manufacturer or retailer page named in the dataset, with the date we read them. Amazon's price at click time may differ; every price on the site carries its source and checked date.
How ordering works
Matches in the Contaminant Finder rank by certified coverage first, then by paperwork grade — never by price or commission. Builder defaults pick the cheapest stage that satisfies the stated requirement (flow, coverage, manufacturer exclusions), and every alternative stays one swap away with its own check results. Products we earn nothing on are recommended on the same terms as products we earn on; two of our whole-house lines currently earn nothing at all.
What the grades mean
Every product carries a paperwork grade (A–C) from the rubric in the certification guide: whole-system performance certification with named contaminants at the top; narrow scopes (TDS-only, taste-and-odor, materials-only) in the middle; component-only or lab-test-only claims at the bottom. A grade describes documentation, not water quality in your home — a C-grade system can filter well; it just hasn't proved it to a certification body.
How we make money
Most buy links are Amazon Associates links: if you buy through one, we earn a commission at no cost to you. Links to manufacturers' own stores are labeled; where a direct program exists but we have not joined it (SpringWell today), the link earns us nothing and is labeled that way in the dataset. Commissions never change a grade, a ranking, or a compatibility result. Full detail: Affiliate Disclosure.