What to drink?

My lo is a year old and I'm just curious on what I should and should not be giving him to drink? We've quit formula and now on milk and food, but if I give him t ok much milk he gets bad constipated.. And too much water is no good right? He drinks ALOT. And pees as much as an adult would (not even kidding, I can change this kid and within 5 seconds of having a clean diaper he looks like he's gone hours without a butt change. So, what do I give him to drink? I don't want to pack him full of sugars, and people keep telling me tea (unsweet, and decaf) causes low iron. I'm so,sorry, I'm a ftm..