The electric utility industry has devoted considerable effort to water management over and above the requirements to meet environmental protection regulations. As of 1982, there were about 40 zero liquid discharge power plants operating in the United States, mostly in the arid western region.1 These plants have gone to zero discharge because of the need to reuse as much water as possible and because of objections over discharging saline water. Most of these power plants employ a brine concentrator (evaporator) to treat waste flow which can consist of ash pond blowdown, cooling tower blowdown, and periodically, demineralizer waste. From this heavily mineralized feed stream, an evaporator can produce ultrapure water suitable for boiler makeup and other uses. Indeed, one of the generating plants in Florida produces a surplus of 300,000 gal/d (1,136 m3/d of marketable ulrapure water.2