Reverse osmosis works by pushing pressurized water against a membrane with pores roughly 0.0001 microns wide, small enough to block dissolved salts, minerals, and most contaminants while letting water molecules pass. The rejected material flushes down the drain as brine. A typical residential RO system stacks a sediment pre-filter, a carbon block, the membrane itself, and a polishing carbon filter, plus a storage tank, because the membrane produces water slowly.
Arizona water is a strong RO candidate because it's hard and high in dissolved solids. Surface water from the Colorado and Salt River projects, blended with groundwater, frequently delivers 16-20 grains of hardness and 400-700 ppm TDS to the tap. RO removes that hardness, sodium, nitrate, arsenic, fluoride, and the chlorine taste a lot of residents don't care for. The result is genuinely clean-tasting water without buying bottles, and that counts for something in a state where summer consumption runs high.
RO isn't a whole-house solution for most homes. Because it sends some water down the drain as brine and puts out slowly, it's almost always installed at a single point of use, usually the kitchen sink with its own faucet, sometimes teed to a refrigerator or ice maker. For whole-house hardness, you pair RO drinking water with a separate water softener or conditioner. The two systems solve different problems, and in Arizona homes they're commonly installed together.
Maintenance is simple but not optional. Sediment and carbon pre-filters need replacing every 6-12 months, faster here because high sediment and hardness load them quickly. The membrane lasts 2-5 years depending on your feed water and whether a softener protects it. Skip the filter changes and chlorine reaches the membrane and destroys it early. A lot of homeowners add a remineralization stage too, since RO strips the good minerals out along with the bad, leaving water slightly acidic and flat-tasting to some folks.
Whether you need RO depends on your goals. If you only want to deal with scale on fixtures and appliances, a softener alone may be enough. If you want better-tasting, lower-contaminant drinking and cooking water, RO is the targeted fix. A water test showing your specific TDS, hardness, arsenic, and nitrate levels is the right place to start, since northern Arizona well water and metro Phoenix municipal water have very different profiles.