Rinse aid
A liquid surfactant added to a dishwasher's dispenser that helps water sheet off dishes during the final rinse, preventing spots and speeding drying.
Rinse aid isn't a gimmick — it's a **surfactant** that lowers the surface tension of water so it runs off your glasses in a thin sheet instead of beading up and drying into spots. It matters most with **[hard water](/glossary/hard-water)** and with modern dishwashers that skip a heated dry to save energy, where it's the main thing standing between you and cloudy, spotty glassware. Keep the dispenser topped up (most have a window or indicator), and turn up the dosing setting if you still see spots. It's a few cents per load and one of the cheapest ways to make a dishwasher's results look new again — more in [keeping your dishwasher cleaning well](/guides/how-to-clean-and-maintain-your-dishwasher).