Choose a tank-style RO system by checking the exact certified reduction claims, the storage tank's usable capacity, feed-water pressure requirements and the cost and availability of replacement stages. Compare a system's performance sheet with your water test and plumbing; NSF/ANSI 58 certification does not mean every model reduces every contaminant. For the broader technology choice, read reverse osmosis vs carbon.
A tank-style reverse-osmosis system stores treated water so it is ready at the dedicated faucet. Choose the unit around its verified claims, your under-sink layout and the service you can maintain.
Verify what the model reduces
Start with a water test or utility report. Then check the exact model in a certifier’s listing and the manufacturer’s performance sheet. NSF/ANSI 58 applies to reverse-osmosis systems, but individual contaminant claims vary by model. The NSF water-treatment standards overview explains why the listing matters.
Compare the parts that affect daily use
| Item | What to check |
|---|---|
| Storage tank | Usable volume and the counter space it occupies |
| Feed-water requirements | Minimum pressure and any limits listed in the manual |
| Faucet and drain | Whether the sink needs a separate faucet hole and drain connection |
| Filter stages | Which cartridges are proprietary and their replacement intervals |
| Water recovery | The maker’s stated production and reject-water information for stated conditions |
Do not treat a nominal tank size or production figure as the exact amount available at every faucet. Pressure, temperature, feed-water quality and tank pressure affect performance; use the maker’s test conditions when comparing models.
Tank or tankless?
A tank can provide stored water during normal use but occupies cabinet space. A tankless unit saves that storage footprint and depends on the model’s rated production and electrical or plumbing requirements. Compare those approaches in reverse osmosis vs carbon for the treatment choice, then read each system’s installation and service manual before ordering.
Browse reverse-osmosis systems.
Common questions
Does a tank-style RO system run out of water?
The storage tank holds a finite supply. Compare its usable capacity and recovery information in the manufacturer's manual with your household's peak use.
Do all RO systems remove the same contaminants?
No. Verify the exact model's certification listing and performance sheet for each contaminant claim you care about.
What should I measure before buying an under-sink RO system?
Measure cabinet width, depth and height, and account for the tank, filters, shutoff valve and space needed to replace cartridges.