What Causes Excessive Thirst And Frequent Urination?

My grandson is Native American Indian. He is 13 years old. He is excessively thirsty, eats very well but does not seem to gain weight, and he urinates frequently and the urine is sticky. When I clean the toilet seat and around the commode, the pee is sticky. He does not eat sweets or drink pop/sweet drinks. He is very conscience about not eating anything sweet such as cake, cookies, etc. He is very active in basketball, biking, and other physical conditioning. When I shared my concern with him, he responds by saying I drink a lot of water, that why I go to the bathroom a lot . Also, he goes to bed early but does not a wake for school unless I wake him. I know that these symptoms could be due to his teen development, yet, I am concerned about the excessive thirst and sticky urine. thank you