When dishes come out spotted or glasses look dull, hard water is one of several possible causes. Hard water leaves mineral deposits behind as water dries on a surface. Detergent residue, overloading, a worn rinse aid setting, and a dirty filter can cause similar results. The goal is to sort these causes so you do not spend money on the wrong fix.
Learn to read the marks
Mineral spots are usually chalky white or hazy, and they feel like a light crust that can be wiped off with a damp cloth or a little white vinegar on a test glass. Etching is different. It looks cloudy with a faint rainbow shimmer, it cannot be wiped off, and it is a change in the glass surface itself. Etching usually comes from detergent chemistry and heat rather than from hardness alone, so it needs a different response. If the marks come off with a mild acid, you are most likely looking at mineral deposits.
Run a simple comparison
Use the same dishwasher for two normal loads. For the first, use your usual detergent and rinse aid, with the same load pattern. For the second, change only one thing, such as the rinse aid amount or the detergent brand. Record which results improve. If spotting persists across both loads regardless of the product, the cause is more likely in the water or in the machine. If one product change makes a clear difference, hard water is less likely the main cause.
Look at the other fixtures
Check the kitchen faucet aerator, the shower head, and the inside of the dishwasher. White crust in those places points to mineral-laden water. Scale in the dishwasher's spray arms, filter, or tub is a strong sign that minerals are in the supply. Clean the filter first, then see whether crust returns after a few weeks. A clean machine that stays clean suggests the problem was loading or detergent rather than the water.
Check the machine's setting
Many dishwashers have a water hardness setting or a rinse aid dispenser that can be adjusted. Find out whether yours has one, and what the manual says about setting it. If you have a reading from your own water test, set the machine to match it. A mismatch between the machine and the actual water can cause spotting even when the detergent is fine.
What softening can and cannot fix
A softener removes the hardness minerals that cause most scale and spotting. It does not remove detergent residue, fix a loading problem, or undo etching already on glass. Expect improvement in mineral spotting and scale, but not a change in etched glass. If you soften the water and the glassware still looks cloudy, check the detergent, the loading, and the machine settings before you assume the softener failed.