Refrigerator and inline filters are the ones most people forget. Most manufacturers rate them for roughly six months or a few hundred gallons, whichever comes first. In Arizona, the higher end of that estimate rarely holds up. Our water carries heavy sediment and minerals that load up the carbon faster, so if your ice tastes off or the dispenser slows down before six months, swap it early rather than waiting on the calendar.
Reverse-osmosis systems use several stages, and each has its own schedule. The sediment and carbon pre-filters protect the membrane and should be changed every 6 to 12 months. The post-filter, which polishes taste right before the faucet, runs on a similar interval. The RO membrane itself is the long-lived part, typically 2 to 3 years, but only if those pre-filters get changed on time. Neglected pre-filters kill membranes early and expensively.
Whole-home cartridge filters sit on your main line and catch sediment before it reaches every fixture. Manufacturers often suggest 3 to 6 months, but that range collapses fast on a well or in an area with heavy sediment. We've pulled cartridges in the Valley and the high country that were packed solid in under three months. If your water pressure drops across the whole house, a clogged whole-home cartridge is one of the first things to check.
Water softeners are different. The resin bed that actually softens the water lasts many years, often a decade or more, so there's no routine cartridge to swap. What you do need to watch is the brine tank and salt level. Check it monthly, keep it topped off, and break up any salt bridge that forms. With Arizona hardness running 12 to 20-plus grains, a softener that runs out of salt quietly stops working long before anything looks wrong.
Arizona water is genuinely hard on filtration. Hardness in the 12 to 20-plus grain range means more dissolved mineral passing through every cartridge, and our sediment-heavy supply loads filters with grit on top of that. The practical upshot is simple: take any manufacturer interval and treat the shorter end as your default. A filter rated for six months in mild water may be doing real work for only three or four months here.
The clearest signs a filter is overdue are slow flow, a change in taste or smell, and fresh spotting on glasses and fixtures. Reduced pressure at a filtered faucet usually means the media is clogged. A return of chlorine taste or a musty odor means the carbon is spent. New white spotting after a softener has been doing its job points to salt or resin trouble. When in doubt, change it. Filters are cheap compared to what they protect.