A. O. Smith AOS-DFRO800 vs Waterdrop G3P800: Which to Buy

The Waterdrop G3P800 and the A. O. Smith AOS-DFRO800 are evenly matched, rated 3.4 and 3.3. The Waterdrop G3P800 leads on filter cost. The A. O. Smith AOS-DFRO800 wins on price and warranty. The A. O. Smith AOS-DFRO800 costs $399.01 less ($449.99 vs $849).

Higher rated

Waterdrop G3P800

#6 in Tankless3.4Full review

For a busy kitchen that wants fast RO water and low waste from a certified system, and can pay for it.

Amazon $849

$849

A. O. Smith AOS-DFRO800

#8 in Tankless3.3Full 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

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 Waterdrop G3P800 for filter cost ($160 a year in replacement filters vs $290 a year in replacement filters).
Choose the A. O. Smith AOS-DFRO800 for price ($449.99 vs $849) and warranty (2-year warranty vs 1-year warranty).

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	Waterdrop G3P800	A. O. Smith AOS-DFRO800
Overall rating	3.4/5	3.3/5
Certification 25%	100 certified to NSF/ANSI 58	100 certified to NSF/ANSI 58
Filter cost 20%	28 $160 a year in replacement filters	0 $290 a year in replacement filters
Water wasted 15%	100 3:1 pure to drain	50 drain ratio not published (neutral score used)
Output 10%	71 800 gallons a day	71 800 gallons a day
Price 15%	5 $849	54 $449.99
Warranty 15%	0 1-year warranty	25 2-year warranty

Independent measurements

Waterdrop G3P800

Tested by	TDS reduction	Output	Pure to drain	Conditions
Water Filter Guru	95.5 %	886.5 gpd	2.2 :1	Tap Score lab: 776 ppm feed to 35 ppm output without remineralization (95.49%). Flow from a 12 oz fill timed at 9.14 s (0.62 gpm) with 58.3 F feed water. Ratio from a 64 oz draw (29 oz to drain); a 12 oz draw measured 1.5:1. Date is the review update date.