Waterdrop G5P500A
#1 in TanklessFull review
For a buyer on a budget who still wants certified RO water with minerals added back.
Amazon $229.99$229.99
The Waterdrop G5P500A is the better under-sink reverse osmosis system overall, rated 3.8 to 3.2. The Waterdrop G5P500A leads on price and filter cost. The Waterdrop G5P500A costs $395.07 less ($229.99 vs $625.06).
iSpring RO500AK
#10 in TanklessFull review
For buyers who want a certified tankless system with remineralization and fast flow. Running costs are high, so it suits households that value the certification over cheap filters.
Amazon $625.06$625.06
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 G5P500A for price ($229.99 vs $625.06) and filter cost ($125 a year in replacement filters vs $196 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 | Waterdrop G5P500A | iSpring RO500AK |
|---|---|---|
| Overall rating | 3.8/5 | 3.2/5 |
| Certification 25% | 100 certified to NSF/ANSI 58 | 100 certified to NSF/ANSI 58 |
| Filter cost 20% | 43 $125 a year in replacement filters | 15 $196 a year in replacement filters |
| Water wasted 15% | 95 2:1 pure to drain | 95 2:1 pure to drain |
| Output 10% | 29 500 gallons a day | 29 500 gallons a day |
| Price 15% | 100 $229.99 | 28 $625.06 |
| Warranty 15% | 0 1-year warranty | 0 1-year warranty |
Specifications
| Waterdrop G5P500A | iSpring RO500AK | |
|---|---|---|
| Filtration | ||
| Output | 500 gallons a day | 500 gallons a day |
| Pure to drain | 2:1 | 2:1 |
| Stages | 8 | 3 |
| Remineralization | Yes | Yes |
| NSF/ANSI 58 | Yes | Yes |
| Other certifications | NSF/ANSI 372 | - |
| Replacement filters | $125 a year | $196 a year |
| Build | ||
| Tank | Tankless | Tankless |
| Booster pump | Yes | Yes |
| Smart faucet | No | No |
| Warranty | 1 year | 1 year |