Abstract: An aqueous solution of an alkali metal silicate and a silicate setting agent containing polyvalent metal ions is mixed with waste material to convert the mixture into a consolidated stable earth-like material substantially insoluble in water. The material is pulverized and mixed with polluted waste water, with the mixture being maintained long enough for the pulverized material to react with pollutants in the waste water to reduce or remove them, following which the suspended solids in the water are separated from it, leaving the water improved in quality; that is, water that is materially less contaminated than before treatment.