You shouldn't use a hot water dispenser that has rust on it because rust can mean that the inside of the dispenser is corroded or damaged, which can make the water dirty. Rust can also change how the water tastes and smells, making it not very nice to drink. If the rust is only on the outside of the dispenser, it might not affect the water's safety or quality, but it can still look bad and be hard to clean. In this case, the dispenser needs to be cleaned often with a mild cleaning solution and a soft cloth or sponge. But if the rust is on the inside of the dispenser, it's best to throw away the whole thing. Rusted hot water dispensers can be dangerous to your health and may not be safe to drink. When it comes to drinking water, it's important to put safety and quality first, so it's best to err on the side of caution and replace the dispenser if the inside is rusted.