Reverse Osmosis vs Whole-House Filters in Arizona
These two systems do different jobs. A whole-house filter treats every tap. A reverse osmosis (RO) system usually sits under the kitchen sink and treats drinking and cooking water.
Why Arizona buyers care: TDS
Phoenix's 2025 report lists total dissolved solids at 464–716 ppm and sodium at 91–183 ppm. EPA's secondary (aesthetic, not health) guideline for TDS is 500 mg/L. High TDS mostly affects taste. Carbon filters don't lower TDS much. RO does.
| Whole-house filter | Under-sink RO | |
|---|---|---|
| Treats | All water in the home | One faucet (sometimes the fridge too) |
| Chlorine taste/odor | Yes (carbon) | Yes |
| Lowers TDS / sodium | Little | Yes, significantly |
| Hardness | No (pair it with a softener) | Yes, at that tap |
| Waste water | None | Some goes to the drain; varies by model |
| Upkeep | Cartridge or media changes | Pre-filters plus a membrane every few years |
Common Arizona setup
Many homes use a softener (or a carbon filter plus a softener) for the whole house, then RO at the kitchen sink. Softened water also helps the RO membrane last longer.
- Under-sink RO: [AFFILIATE LINK: Amazon-or-USWater-RO]
- Whole-house carbon: [AFFILIATE LINK: Aquasana-or-SpringWell-whole-house]
- Replacement filters: [AFFILIATE LINK: Amazon-replacement-filters]