My 2yr old son is always thirsty and drinks his sippy cup sraight down sometimes non stop then wants more. why could that be?

See below: Could just be normal toddler behavior, but if he is eating a lot and peeing a lot, and seems listless or is loosing weight, having him checked for diabetes is warranted.

Be seen: He should be seen by his physician. It is possible it is due to diabetes.

Habit vs problem: Some kids take to a cup and drinking as a play activity.The more they drink, the diluter their urine and the more their body tells them to drink.If he's not getting up at night to drink and can handle a 2 hour drive without, he's probably a habit drinker. If he really has to drink ALL the time, have his doc evaluate him.