Why does my dishwasher leave spots on my glasses?

The spots that may appear on glassware after it is washed and air-dried are caused by harmless minerals (usually calcium, magnesium, and/or silica) that remain on the glass when the water evaporates. Dishwasher deposits can be minimized by using a commercial conditioner, liquid detergents, and using the air-dry instead of the power-dry setting on your dishwasher, which bakes the carbonates onto glassware. Commercial products are available that allow the water to drain from the glassware more completely.