Although lead is a known poison, the mechanical and chemical characteristics of the metal continue to keep lead as an important component in many products. In water supply, lead's durability and workability made it preferable for use as water pipes (as compared to, for example, iron pipes). Lead alloys (bronze, brass) are used for plumbing fittings, and lead solders were also preferred. While state and local governments began to prohibit installation of lead pipes early in the twentieth century, lead alloys continued to be used. Alternative pipe materials have been iron, copper, and later plastics. Although new lead pipes weren't installed later in the 20th century, some existing lead pipes remain in service in many cities.