This is the oversimplistic and chidlike stupid frame reference you operate under, not I.
Since I believe pretty much everything has positives and negatives I would prove nothing I claim by going without water unless I had drunk too much of it or it was sewage or something like that.
Otoh, by you drinking water and me smoking until one of us is hospitalized, you would indeed learn that good for you is not an absolute statement and you would no longer ask stupid non-absolute questions expecting absolute answers. All the while mistaking it for some sort of challenging intellecual exercise.
Put your money where your mouth...if water simply good for you, you should be able to win this bet.
Water=Good
Smoking=Bad
Such is the stupid and inaccurate world view of Blake...