1. The clearest one is limescale building up on elements increases energy costs. 1mm of limescale causes 7.5% increase in energy costs.
2. Equipment repair and servicing schedules are increased. For example, boilers might need repairing once a year in hard water areas compared with once every 3 years in soft water areas. Why a green issue: two visits by boiler engineer per problem, chemicals to do a clean of limescaled and/or replacement parts.
3. Equipment failure. Similar to the above but this time the whole boiler, shower etc is condemned and replaced. Engineers are too expensive to have them repair electric showers. Much cheaper to replace the shower on the first visit.
4. Cleaning chemical usage is increased where limescale is untreated. Chemicals need high levels of carbon to create them.