I get this question on a daily bases. Customers complaining about there dishes not getting clean.
Soft water is highly recommended. It helps the dishwasher perform as designed. Test for hard water and purchase a water softener if necessary. Scrape the dishes off before putting them in the dishwasher. A restricted wash system results in immediate filming and unsanitary conditions. Do not wash your dishes before washing your dishes. Don’t confuse scraping with washing. We need dirty dishes to get clean dishes. The detergent needs the dirty dishes to break down soil as it should.
Always purge the hot water at the sink until it is hot just before running the dishwasher. This will ensure the first fill is hot. Also, check to make sure that your hot water heater is set between 120-125F degrees. Most units are shipped turned way down. Keep in mind that hotter is not better. Any hotter with dishwashers and you get what is called flash drying. This is when the environment in the dishwasher is so hot that after the final rinse, instead of the water running off the glass taking with it all its impurities, it is instantly baked on.
Don’t use a detergent that has a rinse aid in it. You can use liquid rinse aid in the dispenser. This causes suds in the final rinse. Plain CASCADE® and a rinse aid in the dispenser are recommended.