Reverse Osmosis in Tucson: Under the Sink or Whole House

Under-sink reverse osmosis typically costs $300–$950 installed and whole-house RO $4,800–$8,000 (HomeGuide). In August 2026, Tucson Water sampling points measured 140 to 645 mg/L of total dissolved solids, median 524, and 61% were over the 500 mg/L taste guideline. RO removes most of those minerals.

What RO removes from Tucson water

An RO membrane rejects most dissolved salts and minerals, the stuff behind chalky film on a kettle and the flat, mineral taste some people notice. That includes sodium, which Tucson Water's 2025 report puts as high as 70.4 ppm, plus the sodium a softener adds. It also reduces arsenic; Tucson Water's water meets EPA's arsenic standard, with a highest 2025 sample of 8.8 ppb against a limit of 10, but some households choose to lower it further (Tucson Water 2025 report). The 500 mg/L TDS guideline is a secondary, non-enforceable standard about taste, not health.

Under-sink or whole-house

Under-sink RO covers drinking and cooking: pre-filters, a membrane, a small tank and its own faucet, $300 to $700 with a tank or $450 to $950 tankless (HomeGuide). Whole-house RO uses a large storage tank and a pump to supply every tap, sized by gallons per day, from $4,800 to $8,000. It suits households that want low-mineral water everywhere, for spot-free glass or appliances, and have room in the garage for the tank.

Waste water and the membrane

Tucson Water notes that some RO units can send up to 10 gallons to the drain for every gallon they produce, and that RO adds salts to wastewater. Newer designs do much better, so compare the stated waste ratio. On unsoftened water in Tucson's harder zones, scale shortens membrane life; a softener or antiscalant ahead of a whole-house RO protects it.

What to compare

• Testing to NSF/ANSI 58, including any arsenic or PFAS reduction claim you care about.
• Waste ratio and daily output.
• Filter costs: HomeGuide lists $20 to $100 for replacement RO filters.
• Space under the sink or in the garage, and a drain.

Plan on pre-filter changes about once or twice a year and a new membrane every few years. Whole-home options and prices are on the water softener cost guide for Tucson.