The fuming of kettles is caused by the presence in the water of

The fuming of kettles is caused by the presence of calcium trioxocarbonate (IV) in the water. This compound is also known as calcium carbonate and is commonly found in hard water. When hard water is heated in a kettle, the calcium carbonate reacts with the heat to form calcium oxide (also known as quicklime) and carbon dioxide gas. The carbon dioxide gas is what causes the fuming or bubbling that you may see coming from the kettle. The calcium oxide also forms a white or grayish powdery substance, known as scale or limescale, which can build up in the kettle and on heating elements over time. This can reduce the efficiency of the kettle and may even cause it to fail over time. Therefore, it is important to descale your kettle regularly if you live in an area with hard water.