D.M.
W.,
Waking 2 to 5 times may seem like a lot, but you're little one is trying to tell you something.
If he's waking up to feed that much at night, he's probably going to bed and not had enough to eat. By substituting water, you're just going to prolong the night wakings for some kind of substance. I did this with my son, and he ended up waking up MORE because he was still hungry. After one night of eight wakings, I was over it.
I would suggest trying to give him one 8oz. bottle before bedtime with his bedtime routine, and fill it up. Let him eat as much as he will and then put him to bed. See how long he sleeps and then gauge it from there. If he's exclusively breastfed, I would check your supply or maybe think about pumping if you don't already. I started to lose my supply at around 10 mos. and even with pumping had to switch to formula.
Is your son eating solids yet, rice cereal? You might have to adjust his feedings during the day so, he sleeps longer at night. Take a look at his bedtime routine and what time you put him to sleep. Just remember to be consistent and not waiver, but if he's waking to feed he needs to be fed.
Good luck.