In general, hard water impairs the functionality of a dishwasher over time. For instance, the mineral salts may gradually react with utensils and form a layer around them. Hard water can also cause scale deposits on the inside of a dishwasher, something that can significantly lower efficiency. In other words, don't use a dishwasher if you only have a hard water supply. However, there's also an option to soften your water before supplying it to the dishwasher. You can install a water treatment filter on your water supply to remove the mineral salts. Even better, some dishwashers have a built-in water softener that removes minerals from water. So, buying such a dishwasher would be easier than installing a whole water treatment system in your plumbing system.