I took my 16 week old lab to go potty and his poop came out like water... he has also been begging for ice cubes (something we normally give him as a treat)... is he OK?

Diarea can be caused by all the ice. Just because your baby wants something it dose not mean you should give it to him. The cold feels good on his gums so my recommendation is to wet a dish towel and put it in the freezer for a half hour and give it to him.. if the diarea continues I would taker her to the vet. It is not uncommon to have a young pup with worms.

He needs to see the vet immediately. Watery diarrhea in a puppy can be due to several problems, most likely some sort of parasite, but parvo is still something you have to consider. With older dogs, you can take more of a wait-and-see approach, but puppies can get really sick really fast.
He is probably running a temperature and the ice helps him feel better.