Much of San Antonio's water comes from the Edwards Aquifer, a limestone formation, and SAWS lists the typical hardness of its water at 15 to 20 grains per gallon, which puts it firmly in the "very hard" range. You can see it on shower glass and faucet aerators. Your dishwasher sees it every cycle, and it slowly changes how well the machine cleans.
This guide covers what hard water does inside a dishwasher, the maintenance that actually helps, and the point where a cleaning problem turns into a repair.
What hard water does inside a dishwasher
Hard water carries dissolved calcium and magnesium. When it is heated and then dries, those minerals are left behind. In a dishwasher that shows up in a few places:
- •On the dishes as a cloudy or chalky film, most visible on glasses and dark plastics.
- •In the spray arms, where scale narrows or blocks the small jets, so parts of the rack stop getting a proper wash.
- •In the filter and sump, where scale combines with food soil into a gritty paste.
- •On the heating element and inside the valves, where it builds up slowly over years.
Minerals also compete with detergent. The detergent spends part of its effort softening the water, which leaves less for the food.
Film or etching? Test before you treat
Cloudy glasses have two very different causes, and the fix for one makes the other worse.
Mineral film is a deposit sitting on the glass. Soak a cloudy glass in white vinegar for a few minutes, then rinse it. If it comes out clear, you are looking at hard-water film, and everything in this article applies.
Etching is damage to the glass surface itself. It doesn't come off with vinegar and often looks like a rainbow sheen or fine lines. Etching is more common with soft or softened water combined with too much detergent and very hot washes. It can't be reversed. If your home has a water softener, read the section on softeners below.
Monthly maintenance that makes a difference
None of these steps need tools beyond what's in a kitchen drawer. Turn the dishwasher off at the control panel before reaching into the tub, and let the element cool if it just ran.
Clean the filter
Most dishwashers sold in the last decade or so use a manual filter that twists out from the floor of the tub, under the lower spray arm. Remove the lower rack, turn the filter cylinder counterclockwise, lift it out, and rinse it under warm running water with a soft brush. If it has a white crust, soak it in warm water with some vinegar first. Reinstall it until it locks. A dishwasher running with a clogged filter recirculates dirty water and leaves grit on everything.
Clear the spray arms
Look at the jets on the underside of each spray arm. Any that are crusted over or plugged with a seed or bit of glass will leave a dirty stripe on that part of the rack. Most arms lift or unscrew off. Rinse them, and clear stubborn holes with a toothpick or a straightened paper clip. Don't enlarge the holes. Check that each arm spins freely by hand once it's back in place.
Run a descaling cycle
A citric-acid dishwasher cleaner, or a cleaner the manufacturer recommends, dissolves scale from the tub, element and plumbing. Run it in an empty machine on the hottest cycle. In hard water, once every month or two is reasonable. Some manuals specifically warn against certain cleaners, so check yours first.
Settings and habits that help
- •Use rinse aid, and keep it topped up. In hard water, rinse aid is what helps water sheet off glassware instead of drying in droplets. Many dispensers have an adjustable dose. If you still see spots, turn it up one step.
- •Check the water hardness setting. Some dishwashers, including many European-designed models, let you enter your water hardness in the settings menu. If yours does, set it to match hard water and the machine will adjust its dosing or rinse behavior. The manual explains how.
- •Run the kitchen tap until it's hot before starting the dishwasher. The first water into the machine then comes in hot, which helps the detergent.
- •Choose a detergent made for hard water. Many pods and powders are. Using more of a detergent that isn't formulated for hard water rarely solves the problem.
- •Don't pre-rinse spotless. Detergent enzymes need some soil to work on. Scrape plates, don't scrub them.
If you have a water softener
Softeners are common in San Antonio for good reason. With softened water, you usually need less detergent than the package suggests, and you may be able to turn the rinse aid down. Too much detergent in soft water is the classic recipe for etching. If your glasses were fine before a softener went in and started clouding afterward, cut the detergent dose before anything else.
If the softener runs out of salt or stops regenerating, you'll see hard-water symptoms come back gradually. Check the salt level before you blame the dishwasher.
When the dishwasher needs a technician
Maintenance fixes the film. It doesn't fix a failed part. Call for service if you notice:
- •Water left in the bottom after a finished cycle, once you've cleaned the filter. That points to a drain pump, a blocked drain hose or a check valve.
- •Dishes coming out cold and wet, or the cycle running far longer than normal. That can point to a heating element, a thermostat or thermistor, or a control fault.
- •No wash sound at all while the machine fills and drains, which can mean a failed circulation pump.
- •Water on the floor. Turn the machine off at the breaker or unplug it, shut the supply valve under the sink, and don't keep running it.
- •A burning smell or a tripped breaker. Stop using it until it's been checked.
Heavy scale can also make the water inlet valve stick or fill slowly, which is usually a single-part repair once it's confirmed. See our dishwasher repair page for what we check on a visit, or our page on Bosch dishwasher repair if you have one of the models with a hardness setting.
Hard water affects the washer and refrigerator too, but in different places. Our guide to washer inlet screens, ice makers and fridge water valves covers those.
Frequently asked questions
Will vinegar in the rinse aid dispenser damage my dishwasher?
Some manufacturers advise against it because vinegar can affect rubber seals over time. Use a proper rinse aid in the dispenser. Vinegar is fine for soaking a filter or a test glass.
How often should I clean the filter with hard water?
Once a month is a good habit for most households, and more often if you run the machine daily or don't scrape plates.
Why are plastic containers still wet at the end of the cycle?
Plastic doesn't hold heat the way glass and ceramic do, so the water on it doesn't evaporate as the load cools. Rinse aid helps, and so does opening the door a few minutes after the cycle ends. Wet plastics on their own aren't a sign of a fault.