First, read the gaining mass link in my signature. That will give you the A-B-Cs of gaining mass.
Water weight IS a part of muscle mass!
The thing you would do differently is to alter the diet to favor careful carb intake timed around your workouts to boost recovery and limit fat gains.
That makes optimal gains slower but tight.
Strength does NOT=muscle
I can gain muscle WITHOUT increasing strength or even decreasing strength.
I won't explaine why, I give classes on that at the university.