A. O. Smith AOS-DFRO800 vs Waterdrop X12: Which to Buy

The Waterdrop X12 is the better under-sink reverse osmosis system overall, rated 3.5 to 3.3. The Waterdrop X12 leads on filter cost and output. The A. O. Smith AOS-DFRO800 wins on price. The A. O. Smith AOS-DFRO800 costs $649.01 less ($449.99 vs $1,099).

Higher rated

Waterdrop X12

#5 in Tankless3.5Full review

For a large household that wants the fastest flow and lowest waste, and will pay a premium for it.

Amazon $1,099

$1,099

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 X12 for filter cost ($173 a year in replacement filters vs $290 a year in replacement filters) and output (1,200 gallons a day vs 800 gallons a day).
Choose the A. O. Smith AOS-DFRO800 for price ($449.99 vs $1,099).

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 X12	A. O. Smith AOS-DFRO800
Overall rating	3.5/5	3.3/5
Certification 25%	100 certified to NSF/ANSI 58	100 certified to NSF/ANSI 58
Filter cost 20%	23 $173 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%	100 1,200 gallons a day	71 800 gallons a day
Price 15%	0 $1,099	54 $449.99
Warranty 15%	25 2-year warranty	25 2-year warranty

Independent measurements

Waterdrop X12

Tested by	TDS reduction	Output	Pure to drain	Conditions
Water Filter Guru	81.3 %	-	-	Tap Score lab: 235 ppm kitchen tap feed to 44 ppm from the X12 faucet (81.28%), Westminster, Colorado city water; output includes the added minerals. Date is the review update date.