Me dog is drinking water but won't eat what could be wrong?

Could be diabetic or have a tooth that is bothering him. I would take him to the vet and get it checked out as soon as possible

Is it new food? My dog use to hardly eat that much with this certain brand we always bought. As soon as we got her a different brand, she's eating so much she's gaining a lot of weight, which now we have to cut back on her intake of the food, but do you see my point/