A method for treating water includes removing a supersaturated sparingly soluble salt via a self-sustaining de-supersaturation process in which the supersaturated water is contacted with a nucleation material that is reused in the process. Supersaturated reject water from reverse osmosis systems may be de-supersaturated, reducing scale formation on downstream water treatment systems and pipelines. The method may be used for treatment of sulfate-contaminated groundwater, and groundwater contaminated via mining and processing of sulfide ores, and in other applications.