Methodology
Last updated November 6, 2026
Every number on this site is either sourced or labelled as an estimate. This page explains the difference, and how a claim gets from a spec sheet to a published page.
1. Primary sources first
For equipment we work from the manufacturer's spec sheet and the NSF/ANSI certification listing for the specific model — 42 for taste and odour, 44 for softeners, 53 for health contaminants, 58 for reverse osmosis. For prices we use published retail and installed-price ranges, and for water problems we use state health department and EPA guidance on private wells.
2. Cost models show their inputs
Installed cost is modelled from visible inputs: equipment price, installation scope (drain, electrical, permit, bypass), consumables per year, and a five-year service reserve. We do not present a single "average cost" as if it were a quote; the range and what it includes are stated on the page.
3. Product selection
We compare certified removal, capacity against household use, five-year cost per gallon, parts availability and warranty. A product earns a recommendation when it meets the stated criteria; it cannot buy a place in a ranking. Every affiliate relationship is disclosed on the page and in the footer.
4. What we have not tested
We do not run a laboratory and we do not install every system we write about. When a claim comes from a manufacturer spec, a certification listing or an installer report, we say which. We do not imply first-hand testing we did not perform.
5. Sources we work from
| Source type | What it decides | How it is cited |
|---|---|---|
| NSF/ANSI listings | Which contaminants a unit is certified to remove | Standard number and model named |
| Manufacturer spec sheets | Grain capacity, flow rate, membrane output | Spec reproduced with the model |
| Municipal water quality reports | Baseline hardness, chlorine, nitrate | Supplier and year named |
| State well guidance | Testing intervals and contaminant limits | State agency named |
| Published parts and salt pricing | Running cost per year | Price band with the month checked |
When two sources disagree, the page says which one it followed and why. A figure that cannot be traced to a document is labelled an estimate, and an estimate is never presented as the price of a specific install.
6. Corrections
If a certification changes or a reader finds an error, we update the article and its "last updated" date. Emailcontact@gutterguardlab.comwith the page and the correction.