Yes, you can use salt in your dishwasher to help with hard water. Hard water contains high levels of minerals, such as calcium and magnesium, which can leave deposits on dishes and glassware during the dishwasher's rinse cycle, causing spots and streaks.
Dishwashers designed to handle hard water typically have a built-in water softener that uses salt to help reduce the hardness of the water. The dishwasher softener system works by exchanging the calcium and magnesium ions in the water with sodium ions from the salt, which helps prevent mineral deposits from forming on your dishes.
If your dishwasher has a water softener, you will find a compartment specifically designated for adding dishwasher salt. Typically, you'll need to add special dishwasher salt to this compartment when the softener is low or depleted. Be sure to check your dishwasher's manual to find the correct procedure for adding salt.
Using dishwasher salt can be especially beneficial if you live in an area with very hard water. It helps to maintain the efficiency of your dishwasher and keeps your dishes and glassware looking cleaner and spot-free.