When hard water is heated it produces limescale, which reduces the efficiency of your appliances and heating system. Pipes and boilers coated in limescale have to work a lot harder for a longer amount of time to heat your home and running water.
This alone can increase your water heating bills by 12%, as well as cause damage to your heating system and to the planet.
In appliances like kettles and dishwashers, limescale attaches itself to heating elements. They will require a lot more energy to heat the water as they need to heat a layer of hard limescale before being able to heat the water.