IRON (or ferrum, as it is called in Latin and from where its chemical abbreviation FE can also be derived) is probably the most well-known metal. It is found in the earth's crust, an entire epoch was named after it and it is an important trace element for the human body. In practice, however, it is not used as pure IRON, but always as an alloy with other metals, i.e. as a result of a fusion. Such an alloy is, for example, stainless steel V4A. Due to its chemical composition (chromium, nickel and molybdenum), it is the only one suitable for ultrapure water and withstands the aggressiveness of water as a pipeline or container. By the way, the iron content in water depends heavily on geological occurrence; 0.01 to 0.03 mg/l is normal in drinking water.