An evaporation based method of treating produced water from heavy oil production. A produced water from heavy oil recovery operations treated by first removing oil and grease to a desired level, preferably to about twenty parts per million, or less. If necessary, the pH is then adjusted, normally downward and by acid addition, to release at least some carbonate alkalinity as free carbon dioxide. Preferably, all non-hydroxide alkalinity is removed, or substantially so, by introducing the feedwater into a decarbonator. Feedwater is introduced into an evaporator, and the feedwater is evaporated to a selected concentration factor to produce (1) a distillate having a small amount of residual solutes, and (2) evaporator blowdown containing residual solids. Distillate may be directly used for steam generation in a once-through steam generator, or polished by ion exchange or electrodeionization prior to feed to a packaged boiler. In either case, 100% quality steam is produced, directly in indirectly, for downhole use.