A hydrogen atom isn't water. Neither is an oxygen atom.
Water is continually and routinely created by several naturally occurring phenomena.
Water is also destroyed when subject to certain conditions.
There was a time on this planet when water did not exist.
Matter can be destroyed. You speak of the natural law of conservation but interpret incorrectly.
Of course the above is moot. As it has already been pointed out "fresh water" does have a definate routine and extremely common meaning as already stated.