«ما من ماء إلا وهو رطب»
There is no water except that it is moist.
This expression contains a negative construction together with an exception introduced by “except.” The resulting sense affirms moisture of all water. Seeing an isolated negative particle is therefore not enough to call the whole statement universally negative.
The principle is to determine quantity and quality from the complete expression. Negation, exception, word order and context must be read together.