@koberulz it's basically the amount of Calcium and Magnesium Carbonates dissoved in the water. I think it has to do with how much limestone is in your local aquifer. Water hardness is a problem for things like boilers, coffee machines and dishwashers because it results in the buildup of scale, or for aquariums and home brewers who need to know the water chemistry.
If you live in #naarm the geology seems to be predominantly sandstone and basalt #CitationNeeded and so the water is quite soft, so unless you keep tropical fish, brew beer or actually read the manual that comes with the dishwasher the water hardness isn't generally anything you need to worry about.