Abstract: Waste water streams from the steam-extraction of heavy oils are treated to remove organic contaminants, suspended solids and mineral contaminants, so as to produce a purified water stream of a quality suitable for reuse in steam production. Suspended solids are removed by coagulation, flocculation and flotation, organic contaminants are removed by activated carbon adsorption, and mineral contaminants are removed by electrodialysis or reverse osmosis and ion-exchange. Thermal economy also is effected by passing the purified water stream in heat exchange relation with the waste water stream after suspended solids removal.