A. O. Smith AOS-DFRO800
#8 in TanklessFull review
For a household that wants fast, certified tankless RO for less than most rivals. Buyers without a spare faucet should get the brushed nickel version.
Amazon $449.99 Amazon $484.99$449.99
The A. O. Smith AOS-DFRO800 is the better under-sink reverse osmosis system overall, rated 3.3 to 3.0. The A. O. Smith AOS-DFRO800 leads on certification and warranty. The iSpring RO800G wins on filter cost. The A. O. Smith AOS-DFRO800 costs $9 less ($449.99 vs $458.99).
iSpring RO800G
#14 in TanklessFull review
For big households that want fast tankless RO with low waste and cheap filters. It lacks the third-party certification of pricier rivals.
Amazon $458.99$458.99
Prices were last checked November 2, 2026 and are subject to change; the price and availability shown by the retailer at the time of purchase apply.
Which should you buy?
- Choose the A. O. Smith AOS-DFRO800 for certification (certified to NSF/ANSI 58 vs no third-party certification) and warranty (2-year warranty vs 1-year warranty).
- Choose the iSpring RO800G for filter cost ($85 a year in replacement filters vs $290 a year in replacement filters).
Scores side by side
Each factor is scored 0-100 against the same fixed reference points for every tankless under-sink reverse osmosis system; a clear win is highlighted. How we rank explains each one.
| Factor weight | A. O. Smith AOS-DFRO800 | iSpring RO800G |
|---|---|---|
| Overall rating | 3.3/5 | 3.0/5 |
| Certification 25% | 100 certified to NSF/ANSI 58 | 0 no third-party certification |
| Filter cost 20% | 0 $290 a year in replacement filters | 67 $85 a year in replacement filters |
| Water wasted 15% | 50 drain ratio not published (neutral score used) | 98 2.5:1 pure to drain |
| Output 10% | 71 800 gallons a day | 71 800 gallons a day |
| Price 15% | 54 $449.99 | 53 $458.99 |
| Warranty 15% | 25 2-year warranty | 0 1-year warranty |
Specifications
| A. O. Smith AOS-DFRO800 | iSpring RO800G | |
|---|---|---|
| Filtration | ||
| Output | 800 gallons a day | 800 gallons a day |
| Pure to drain | - | 2.5:1 |
| Stages | 2 | 2 |
| Remineralization | No | No |
| NSF/ANSI 58 | Yes | No |
| Other certifications | NSF/ANSI 372 | - |
| Replacement filters | $290 a year | $85 a year |
| Build | ||
| Tank | Tankless | Tankless |
| Booster pump | - | Yes |
| Smart faucet | No | No |
| Warranty | 2 years | 1 year |