Why do drinking glasses get cloudy in the dishwasher?

There are two completely different reasons glasses go cloudy in the dishwasher, and the fix for one makes the other worse — so it’s worth knowing which one you’re dealing with.

The first is hard-water filming. If your water has high levels of dissolved calcium and magnesium, the dishwasher’s heat bakes those minerals onto the glass surface as the water evaporates during the drying cycle. This leaves a whitish, chalky haze. A quick test: rub the cloudy spot with a little white vinegar on a cloth. If the haze wipes away, it’s mineral buildup. Fix it by adding a rinse aid to your dishwasher (it helps water sheet off instead of evaporating in place) and occasionally running an empty cycle with a cup of white vinegar in the top rack.

The second cause is etching — and this one is permanent. Etching happens when you use too much detergent, especially with soft water. Excess detergent is mildly abrasive; over dozens of cycles, it microscopically pits and roughens the glass surface, which scatters light and creates a cloudy look that won’t wipe off. The only fix is prevention: use less detergent (soft-water areas may need as little as a tablespoon), skip the heated dry cycle, and don’t pre-rinse dishes — modern detergents need some food residue to buffer their alkalinity.