This is not true. Hydration can help with blood oxygen levels which can help someone recover from AS, but AS itself is much more complex than purely being a hydration matter and some people are more genetically predisposed to AS than others. Over hydration can be counter productive, though, dehydration may intensify the effects of AS.
Increasing your Nitric Oxide levels ahead of exposure to altitude can be beneficial but no guarantee. Beet Juice is commonly used, but pomegranate juice and 100% dark chocolate may help as well. This is something that needs to be pregamed weeks in advance and the difference may be negligible to none for some people.