Hard water can affect how well your dishwasher cleans

After cleaning, do glasses emerge from your dishwasher cloudy or spotted? Is there a whitish crust on your dishwasher's heating element?

If yes, you might think there's something wrong with your dishwasher. But the problem could be caused by hard water, which has a total level of calcium, magnesium, and other minerals at 7 grains per gallon or 121 milligrams per liter or higher. Hard water can not only lead to the spotting and crusted-over heating element but also diminish how well your dishwasher cleans. Other possible signs of hard water include a filmy residue on shower/bath surfaces; mineral buildup on appliances that use water, like a coffeemaker; and decreased sudsing of soap and detergents—you might have trouble lathering up in the shower, for instance.

To determine the hardness of your water, contact your water company. Or if you don't have municipal water, use a home test kit, which you can pick up for $10 to $25 at a home center or hardware store. The map on this page from the U.S. Geological Survey shows where calcium carbonate, a component of hard water, is most common.

If you have hard water, you might consider installing a water softener; a local water-softener dealer might even do a free analysis of your water. (Some Miele dishwashers have a built-in water softener, to which you add dishwasher salt.) And to help your dishwasher work at its best:

Use the right amount of detergent. Refer to your owner's manual for details. The harder your water, the more detergent a load needs. GE suggests that you calibrate a model with its SmartDispense feature according to water hardness so that the proper level of cleaner is dispensed. And if you do install a water softener, refer back to your manual again to figure how much less detergent you should now use.

Add rinse aid. To prevent the common hard-water problem of spotting and to help dishes dry better, most makers recommend that you add a rinse aid. Again, check the owner's manual. Some models let you adjust how much you can add.

Clean it out. If you see white residue inside your dishwasher, you can occasionally try to dissolve it with distilled white vinegar. Instead of using detergent, place a container with 2 cups of vinegar in the bottom rack and run a normal cycle but without drying.

—Ed Perratore

Essential information: If you need a new dishwasher, try to take advantage of cash for appliances rebates and other incentives. Use our free buyer's guide to dishwashers and check our recently updated ratings of dishwashers (available to subscribers). Our August 2010 report on dishwashers will be online and on newsstands tomorrow, part of our special section on kitchen remodeling.