incrustant adjective 1noun 1forms 3 adjective1 •Tending to leave an incrustation on a boiler or other container when the containing water evaporates.It is the practice at the Columbus plant to leave between 25 and 40 parts per million incrustant hardness in the water. — 1915 noun1 •Any substance that is dissolved in water which forms an incrustation when the water evaporates.The total incrustants in the water, expressed in terms of calcium carbonate, are clearly the sum of their component bases, calcium and magnesium, expressed in terms of calcium carbonate. — 1905 formsincrustants · more incrustant · most incrustant