Hardness of water
Water where you live might be hard or soft, it depends on the rocks your water meets on its way to you.
Hard water makes scum and scale
1) With soft water you get a nice lather with soap. But with hard water you get a nasty scum instead- unless you're using a soapless detergent. The problem is dissolved calcium ions and magnesium ions in the water reacting with the soap to make scum which is insoluble. So to get a decent lather you need to use more soap- and because soap isn't free, that means more money going down the drain,
2) When heated, hard water also forms furring or scale ( mostly calcium carbonate) on the insides of pipes, boilers and kettles. Badly scaled- up pipes and boilers reduce the efficiency of heating systems, and may need to be replaced- all of which costs money. Scale can eventually block pipes.
3) Scale is also a bit of a natural thermal insulator. This means that a kettle with scale on the heating element takes longer to boil than a clean non-scaled up kettle- so…