The categories of water and what defines each
Into how many categories do the four imams divide water, and what defines each?
Water divides into five categories: pure and purifying without dislike, which is absolute water; pure and purifying but disliked, such as water left over by a cat; pure but not purifying, which is used water; impure water; and water whose purifying quality is doubtful, such as water left over by a donkey or a mule.
Water divides into absolute tahur, valid for purification; mixed water, pure but not purifying; and impure water altered by najasah.
Water divides into tahur; pure but not purifying, being used water or water altered by a pure substance; and impure water.
Water divides into three categories: tahur, which removes hadath; pure, which does not remove hadath; and impure water.