Not what the box says. What the certifier's listing says — with the figures, the standard numbers, the gaps, and what a year of filters really costs.
Why this page exists. A site called The Water Math that recommends products on the strength of marketing copy would be a site that does not do its own math. So we went and read the listings.
Some of what came back was uncomfortable. One product we used to put first for documented lead turns out to hold no certification from anyone — and the third-party testing its maker does cite covers the two stages that are not the lead filter. We changed the recommendation. That is what this page is for.
"Certified to NSF/ANSI 53" means a certifier — NSF, IAPMO R&T or the WQA — tested a named model, published a listing you can look up, and audits the factory. You can verify it yourself in a public database.
"Tested to meet NSF/ANSI standards" means a laboratory ran a test once. It may be an excellent test. There is no listing, no named model, no audit, and nothing for you to check.
"NSF/ANSI 372 certified" means the unit's own parts contain almost no lead. It says nothing whatsoever about removing lead from your water. This one is misread constantly, including in retail listings.
Pitcher · carbon + ion exchange · point-of-use
The only product on this page whose paperwork actually names the contaminants people buy it for. It is also the one whose famous selling point — the "000" reading on the TDS meter — is not a certified claim.
IAPMO R&T certifies the 5-stage filter together with its compatible pitchers against NSF/ANSI 42 (chlorine taste and odour) and NSF/ANSI 53 (health effects). Rated capacity: 15 gallons per filter.
| Certified reduction claim | Figure |
|---|---|
| Chlorine taste & odour (NSF/ANSI 42, 2.0 mg/L challenge) | 99.4% |
| Lead, pH 6.5 / pH 8.5 (0.15 mg/L challenge) | 98.9% / 98.8% |
| Hexavalent chromium, pH 6.5 / pH 8.5 | 99.4% / 99.5% |
| Mercury, pH 6.5 / pH 8.5 | 96.6% / 94.2% |
| PFOA and PFOS (0.0015 mg/L challenge) | 99.8% |
| Replacement filter (4-pack, $59.99) | $15.00 each |
| Certified capacity per filter | 15 gallons |
| At ½ gallon a day → about 12 filters a year | ≈ $180/yr |
There is no published replacement interval — the manufacturer tells you to replace when the meter reads 006 or higher, and states the warranty does not guarantee any particular filter life. On high-TDS water it will be materially more than $180. This is the number that decides whether the pitcher is cheap.
See it on Amazon →Sources: Culligan ZeroWater performance data sheet · manufacturer FAQ
Under-sink reverse osmosis · point-of-use
A capable machine whose certified performance table contains exactly one line. Everything else printed on the box is real laboratory testing, but it is not certification, and the difference is the whole point of this page.
IAPMO R&T, not NSF, certifies model WD-G3P800 against NSF/ANSI 58 and NSF/ANSI 372. Standard 372 is a rule about the lead content of the unit's own wetted materials (≤0.25%) — it is not a claim that the unit removes lead. Retail listings for this model disagree with each other about standards 42 and 53, and we could not settle that at a certifier database.
| Certified reduction claim | Figure |
|---|---|
| Total dissolved solids (750 mg/L challenge; standard requires ≥75%) | certified |
| Sediment/carbon pre-filter (6 months) | $29.99 × 2 |
| Carbon block filter (12 months) | $29.99 |
| RO membrane (24 months) | $129.99 ÷ 2 |
| Total per year | ≈ $155/yr |
| Wastewater | 1 cup to drain per 3 cups produced |
Waterdrop publishes about $155 a year itself, which matches the arithmetic — a rare case of a manufacturer's running-cost figure holding up. Electricity is a few dollars on top.
See it on Amazon →Sources: Waterdrop product page · certification wording and performance data sheet in the WD-G3P800 manual · NSF certified products database (no NSF/ANSI 58 listing found for this brand)
Whole-house / point-of-entry · 3-stage
We used to put this first for documented lead. After checking the listings, we do not any more. Nothing here is a claim that the filter fails — it is a statement that no certifier has ever verified the thing you would be buying it for.
No listing exists with NSF, IAPMO R&T or the WQA for any WGB whole-house model. iSpring does hold genuine NSF/ANSI 58 certification — on its RCC7 and RO500 reverse-osmosis systems, which are different products. Home Depot's own specification table for this model reads "No Certifications or Listings".
| 3-stage replacement set (F3WGB32BPB) | $211.99 |
| Manufacturer replacement interval | every 6–12 months |
| Per year, at 12 months | $211.99 |
| Per year, at 6 months | $423.98 |
Our calculator uses the 12-month figure. If your water is sediment-heavy you will be at the top of that range, which changes the payback arithmetic considerably.
See it on Amazon →Sources: NSF listings for iSpring (14 products, all RO) · Home Depot specification table · manufacturer product page
Whole-house / point-of-entry · iron & manganese
Also uncertified — but here that matters less, and we will say why rather than pretend the two cases are the same.
No listing with NSF, IAPMO R&T or the WQA. The published figures — iron 3.0 → 0.01 ppm, manganese 1.0 → 0.01 ppm — are the manufacturer's own. A third-party SGS test from 2018 is cited by some retailers; that is a lab test, not a certification.
| 3-stage replacement set (F3WGB32BM) | $159.99 |
| Iron/manganese cartridge life | 50,000 gal |
| Other two cartridges | 100,000 gal each |
| Per year, at 12 months | $159.99 |
| Per year, at 6 months | $319.98 |
The iron cartridge lasts half as long as the other two, so on genuinely rusty water you are replacing the expensive part twice as often as the headline set price suggests. Why we are more relaxed about certification here: iron and manganese are staining and taste problems, not the health contaminants that certification programmes were built to police. The failure mode is orange laundry, not a health risk you cannot see. That is a defensible place to accept a manufacturer's number — lead is not.
See it on Amazon →Sources: NSF listings for iSpring · manufacturer product page · retailer listings
The calculator now routes documented lead and PFAS to the certified pitcher rather than to the whole-house system or the reverse-osmosis unit, because it is the only one of the three with a listed certification naming those substances.
For arsenic and nitrate it now says the thing we did not want to have to say: none of our picks is certified for either, and it sends you to the NSF database to find one that is. We would rather lose the sale than sell you a maybe.
The yearly filter costs in the calculator have been corrected upward where our earlier figures were too low — most sharply for the whole-house lead system, from $150 to $212 a year.
Run the calculator →