Waterdrop TK-FS
The Waterdrop with fluoride filters in the box. Costs $80 more than the TK-A, which can take fluoride filters as an add-on.
Amazon $239.99$239.99
The Waterdrop TK-FS is the better gravity water filter overall, rated 3.3 to 3.1. The Waterdrop TK-FS leads on certification. The Purewell 2.25G 3-Stage Window wins on value. The Purewell 2.25G 3-Stage Window costs $81 less ($158.99 vs $239.99).
Prices were last checked November 9, 2026. Product prices and availability are accurate as of that date and are subject to change; the price and availability shown on Amazon or the retailer's site at the time of purchase apply. As an Amazon Associate we earn from qualifying purchases.
Purewell 2.25G 3-Stage Window
The 3-stage Purewell with a water-level window. It costs a little more than the certified PW-OB.
Amazon $158.99$158.99
Which should you buy?
- Choose the Waterdrop TK-FS for certification (states certification to NSF/ANSI 42, NSF/ANSI 372 vs no certification or test claim published).
- Choose the Purewell 2.25G 3-Stage Window for value ($70.66 per gallon of capacity ($158.99, 2.2 gal) vs $106.66 per gallon of capacity ($239.99, 2.2 gal)).
Scores side by side
Each factor is scored 0-100 against the same fixed reference points for every up to 2.25 gal gravity water filter; a clear win is highlighted. How we rank explains each one.
| Factor weight | Waterdrop TK-FS | Purewell 2.25G 3-Stage Window |
|---|---|---|
| Overall rating | 3.3/5 | 3.1/5 |
| Value 25% | 53 $106.66 per gallon of capacity ($239.99, 2.2 gal) | 79 $70.66 per gallon of capacity ($158.99, 2.2 gal) |
| Running cost 15% | 75 $0.012 per gallon filtered ($34.99 per element, 3,000 gal each) | 50 replacement cost or element life not published (neutral score used) |
| Capacity 15% | 17 2.2 gal tank | 17 2.2 gal tank |
| Certification 20% | 40 states certification to NSF/ANSI 42, NSF/ANSI 372 | 0 no certification or test claim published |
| Element life 15% | 100 3,000 gal rated per element | 100 3,000 gal rated per element |
| Warranty 10% | 11 1-year warranty | 0 warranty not published, scored as none |
Specifications
| Waterdrop TK-FS | Purewell 2.25G 3-Stage Window | |
|---|---|---|
| Capacity and flow | ||
| Tank capacity | 2.2 gal | 2.2 gal |
| Price per gallon of capacity | $106.66 | $70.66 |
| Elements included | 4 | 2 |
| Maximum elements | 4 | 2 |
| Flow, as shipped | - | 4 gal/hr |
| Filtration | ||
| Element type | Coconut shell carbon filter (black) | Black carbon composite: 0.01 micron UF membrane, silver ion membrane and carbon block |
| Certified | NSF/ANSI 42, NSF/ANSI 372 | None stated |
| Certification detail | Listing: system certified to NSF/ANSI 372 and the black carbon filter to NSF/ANSI 42. The listing does not say the fluoride filters are certified. | Listing makes no certification claim for this model. |
| Fluoride | Included | - |
| Fluoride element life | 1,000 gal | - |
| Running cost | ||
| Rated life per element | 3,000 gal each | 3,000 gal each |
| Replacement element | 35 $ | - |
| Cost per gallon filtered | $0.012 | - |
| Build | ||
| Material | 304 stainless steel | 304 stainless steel |
| Height | - | 20 in |
| Diameter | - | 8.8 in |
| Warranty | 1 year | - |