How much more water should i drink a day while taking concerta?

Same as always: For a male your age the institute of medicine recommends at least 98 oz fluids daily (actually 3 liters). Could be all water, or combination of juice, water, etc. Best not to use caffeinated liquids since they interact adversely with the methylphenidate (active ingredient of concerta). Using Concerta doesn't increase the need for fluids, it just may cause dry mouth in some people.