MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY MARTYN F. CHILLMAID / SCIENCE PHOTO LIBRARY
Water hardness test. Permanent hard water does not change when boiled, and the water here has remained clear. Permanently hard water is caused by calcium and magnesium sulphates or chlorides that are not precipitated out of solution during boiling, unlike the calcium carbonate that forms when temporarily hard water is boiled.
Model release not required. Property release not required.