Leviticus 11:35-36 NASB
35 Everything, moreover, on which part of their carcass may fall becomes unclean; an oven or a [t]stove shall be smashed; they are unclean and shall continue as unclean to you. 36 Nevertheless a spring or a cistern [u]collecting water shall be clean, though the one who touches their carcass shall be unclean.
It would seem almost all things that came into contact with an unclean carcass were defiled by it,but when it came into contact with water it seems the water was never defiled.
Why was water never defiled by an unclean carcass?