Why Is My Son Drinking A Lot During The Day?

Hi, My son Is 2yrs. old and drinks way too much during the day. He used to drink a gallon a day of milk, I started monitoring his intake. Cut back by changing to 2%., but he was still begging for something to drink. So I started watering it down, still begging til it s gone again. So I started given him other drinks. Well he really doesn t care want he is drinking as long as he drinks. He is at 91 % height and weight, he looks perfect in shape for his size. I think their is something I m missing. He is always asking/and getting more. And he is a very healthy eater to. I own a daycare, and we eat very healthy(on food program). He loves all fruits and veg., and meat. I can eat any kind of bread like he has not seen it for a while. Most people would beg for a child who doesn t complain, but it seems unhealthy and i concerned. His Doc says don t worry when he get full he ll stop. I still waiting for that day, and in two wees he ll be 3yrs old. confused in Indaina