White residue on dishes may be poorly rinsed detergent, hard-water minerals, or a combination of both. Useful clues include whether the film dissolves with vinegar on an acid-safe item, whether it is strongest on glass, and whether the machine has adequate water, temperature, and rinse aid for the cycle.
Separate detergent powder from mineral film
A powdery deposit near the dispenser can point to poorly dissolved detergent or a dispenser door blocked by dishes. A uniform chalky film over many items fits hard water more closely.
Review detergent amount and type
Too much product can leave residue, especially with small loads or relatively soft water. Use the amount recommended for your water hardness and machine rather than filling the cup by habit.
Check spray arms, filter, and loading
A dirty filter, blocked spray holes, or dishes that prevent an arm from rotating reduce rinsing. Clean accessible parts according to the manual and leave space for water to reach surfaces and the dispenser.
With hard water, rinse aid and descaling can help
If the film is mineral, adjust rinse aid and dishwasher salt when the model uses them and descale as the manufacturer directs. Do not mix acids with bleach or other cleaners inside the machine.