Does adding lemon juice to water chemically alter its nutrients and thereby negating any of its health benefits?
Does water really chemically alter the nutrients in lemon juice rendering a lemon drink of no health benefit whatsoever other than the obvious water base?


No, of course not. Otherwise, humanity would have succumbed to scurvy a long time ago. 

I encourage you and your friend to visit PubMed where you can peruse hundreds of refereed abstracts of studies that illustrate that nutrients from citrus fruits are bioavailable to humans and other species and necessarily require administration with water.

Here is a one-pager on lemon juice from the Cleveland Clinic, which is probably a reliable enough source in this case if you want to skip the more technical items at PubMed.