cutting back on carbs WILL work. but that will also effect your results.
ways to reduce water without effecting gains=
drink as much water as you can, sip it all day long.
take in lots of fruits and vegetables.
take cranberry extract and milkthistle
Yes, but most guys eat more carbs than they need...when I say most I mean most all.
I know you equate gains to size gained...at least that's what most of your post imply...and that's fine, if that's what matters to you or any other person...but size gains to me are not everything.
Another thing about the carbs, the types of carbs he's eating could have a huge impact on this. For instance, something I noticed a few a couple years ago, I can eat the same amount of carbs every day...lets just say 300g because that's an easy number to work with...if a large portion of those carbs are coming from rice, doesn't matter if it's brown or white, I hold more water and I'm more bloated. If I was to eat 150g of carbs from rice per day, half my daily carbs if I was eating 300 carbs, I'd be bloated and watery as crap.
For that reason, I don't eat a lot of rice...hardly any at all unless it's a cheat meal with some Chinese food or the occasional "regular" meal in the wk that might have some rice, but it's rare. I do much better with oats...which is actually my prime source for carbs...a little potatoes and some waxy maze, that's it...not counting vegetable carbs.