Why your dishwasher leaves spots and how to stop it

Spots and cloudy residue on glasses and dishes are one of the most common dishwasher complaints, and the good news is that most causes have a simple fix you can try before assuming something's broken. Here's what's usually behind it.

Hard water is the most common culprit

San Francisco's water is moderately hard, which means it carries dissolved minerals like calcium and magnesium. As water evaporates off dishes during the drying phase, those minerals get left behind as a white, chalky residue, especially visible on glassware and dark dishes.

This isn't a sign anything is wrong with your dishwasher. It's a water chemistry issue, and it's addressed with the right detergent and settings rather than a repair.

The fix: rinse aid

Rinse aid is the single most effective fix for spotting. It changes the surface tension of water during the final rinse, causing it to sheet off dishes in a thin film rather than forming droplets that dry into spots. Most dishwashers have a small rinse aid dispenser near the detergent compartment, and it typically needs refilling every few weeks depending on how often you run the machine.

If you've never used rinse aid, adding it is often enough to solve the problem entirely within a few cycles.

Check your dishwasher's water hardness setting

Many dishwashers have an adjustable water hardness setting that changes how much detergent and rinse aid the machine uses. If this is set too low for your actual water hardness, the machine won't use enough of either to fully address mineral deposits. Check your owner's manual for how to adjust this setting, and consider setting it slightly higher if spotting persists.

Water temperature matters more than you'd think

Dishwashers rely on hot water, generally 120°F or higher, to fully dissolve detergent and rinse aid and to help water sheet off dishes cleanly. If your water heater is set lower than that, or if you run the dishwasher right after a shower has used up the hot water, spotting can get worse. Running the kitchen faucet until the water runs hot before starting the dishwasher ensures the first fill isn't lukewarm.

When it's not water chemistry

If you've tried the above and spotting continues, or if you're also noticing dishes coming out with actual food residue rather than just mineral spots, the issue may be mechanical. A clogged spray arm, a failing water inlet valve, or a heating element that isn't reaching proper temperature can all cause washing problems that look similar to spotting at first glance. That's when it's worth having a technician take a look rather than continuing to troubleshoot water chemistry.

If you've worked through this checklist and dishes are still coming out spotty or dirty, see our dishwasher repair page for the mechanical issues we most commonly find and fix.

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