Hey 918, there are various sources on what drinks are actually hydrating and which are diuretic/dehydrating - you’ll find various opinions through Google search. In general, drinks with caffeine, sugar and alcohol are diuretic, and apparently (I was sad to find out from a nutritionist) several herbal teas (detox teas, hibiscus, and others) are somewhat diuretic also.
That said, when it comes to collagen and elastin, my understanding is that those things are genetic. For example, “showers” have more collagen - their dicks don’t change as much from soft to hard because collagen doesn’t expand like elastin does. “Growers,” on the other hand have more elastin and less collagen, so our dicks get smaller because we don’t have as much collagen to hold the shape, but therefore have more elastin to allow the elastic growth. I’m not sure how this interacts with hydration though.
I’m also a grower, but have had flaccid gains. I’ve always been pretty good about staying hydrated, but when I learned on here about the importance of hydration for flaccid size (more hydration = more blood in your body = more blood available to flood your dick), I’ve made hydration an even greater priority. I enjoy occasional coffee and wine, but agree to offset each cup or glass with an EXTRA glass of water than I’d otherwise have had.