Pure water is that which is pure in itself and can purify anything else.
Impure water is neither useful for Ghusl , complete bath, nor for ablution. And We send down pure water from the sky. The water mentioned above should be free of color, taste or smell. If a color, taste or smell is noticed in the water, even if these things are pure, the water cannot be used for purification. Water which is already used for purification may be used again if it is still pure.