If you live in an area with hard water then you TOTALLY know what I'm talking about. You put your dishes in the dish washer only to have them (it seems) come out looking dirtier than when they went in.
Sure you can hand wash your dishes and prevent a lot of the problem, but who wants to do THAT all the time? (Answer...NOT me!!)
Do I hear some of you out there who know our family quite well snickering? You're thinking, "Wait...she doesn't do the dishes in her home!" And you would mostly be right. When I'm cooking or baking, I actually do a fairly good job of cleaning up after myself including washing dishes as I use them. Everything that I wash is hand-washed. I don't mess with the dishwasher. My husband does that! Still, I have to use the dishes that he washes in the dish washer & BOY HOWDY do they come out needing help in this hard water!
There are a couple of ways to clean dishes with hard water. The easy (but not nearly as effective) way is to put a cup of vinegar in the dishwasher & run a load of clean (other than the hard-water stains) dishes. Don't put soap or anything else in; just the vinegar. However, it may take a couple of loads to get them all clean.
The other way is to fill your sink with vinegar & drop in the clean dishes with hard-water stains. Let them sit overnight. In the morning, rinse & dry them. Viola! They'll be clean!
You can help prevent the hard-water stains by using vinegar as your rinse aid all the time. Just put it where you normally would the (expensive) store-bought rinse-aids. A bonus to using the vinegar as a rinse-aid is that it also helps keep your dishwasher lines clear and free of gunk! Some people also add a lemonade packet (without anything added) to their detergent mix to help with hard-water stains. I have not personally tried that, though.
Some people have reported that their water is so hard that vinegar just in the rinse-aid container isn't enough. They actually add from 1/2 cup to every load of dishes to keep them clear. Others say that they just add that 1/2 cup all the way up to a full cup every 3-5 days & that this in addition to the vinegar as a rinse aid is enough to keep their dishes clear..