Reverse osmosis system vs Under-sink filter
Choose reverse osmosis if you need to remove fluoride, arsenic, or nitrate — it is the only one that does. Choose a standard under-sink carbon filter if your main concerns are lead, chlorine, and VOCs, and you want higher flow with no water waste.
| Reverse osmosis system | Under-sink filter | |
|---|---|---|
| Best for | You want the most thorough filtration — the only common type that removes fluoride, arsenic, and dissolved solids. Accept some water waste. | You want strong contaminant reduction at the kitchen tap without a countertop unit, and are comfortable with a simple under-cabinet install. |
| Typical cost per gallon | ~20¢ | ~6¢ |
| Removes fluoride / arsenic | Yes | No |
| Most contaminants certified | up to 17 | up to 14 |
| Installation | Under-sink system with a dedicated faucet and storage tank. | Mounts under the sink; connects to the cold line. Basic DIY. |
| Filter changes / year | ~1 | ~1.5 |
| Certified models we track | 130 | 764 |
Still not sure? The right choice depends on what's actually in your water. Look up your ZIP to see your contaminants, then pick whichever type is certified to remove them at the lowest cost per gallon.
Frequently asked
Is reverse osmosis system or under-sink filter better for lead?
Both can be certified for lead — what matters is the specific model's certification, not the category. Look for NSF/ANSI 53 lead certification on the exact model. We list the certified claim for every filter.
Which is cheaper over time?
Compare cost per gallon, not sticker price. Here, Under-sink filter is typically cheaper per gallon (~6¢ vs ~20¢), because the running cost of replacement cartridges usually outweighs the upfront price.