the boiler feedwater used in the steam boiler is a means of transferring heat energy from the burning fuel to the mechanical energy of the spinning steam turbine. the total feed water consists of recirculated "condensate" water and purified "makeup water". because the metallic materials it contacts are subject to corrosion at high temperatures and pressures, the makeup water is highly purified before use. a system of water softeners and ion exchange demineralizers produces water so pure that it coincidentally becomes an electrical insulator, with conductivity in the range of 0.3–1.0 microsiemens per centimeter. the makeup water in a 500 mwe plant amounts to perhaps 120 us gallons per minute (7.6 l/s) to replace water drawn off from the boiler drums for water purity management, and to also offset the small losses from steam leaks in the system.