Sorry to contradict you, David, but at least one form of water hardness CAN be removed by boiling.(posted 8271 days ago)
Water hardness can be caused by a number of dissolved minerals, but one of the most common forms of hardness is due to dissolved Calcium Carbonate and Carbon Dioxide. This is called 'temporary' hardness because the CaCO3 can be precipitated out by heating or boiling the water.See this link for a fuller explanation.