S.G.
I was told one ounce per month - so 13 oz. water.
I would usually make a bottle/cup in the morn with the amount of water and let my baby drink from it all day til gone.
You might try a combination of fruit juice (apple or white grape) diluted. Maybe start with 1/2 or 3/4 juice and 1/4 to 1/2 water to get him to drink it. And, then everyday start adding more water until you get to all water. Not everyone likes plain water, so you may never convince him. You may have to put a little juice or squeeze of lemon or something in it.
Good luck.