Hi Lily's mom,
I think it's good if your lo wants to drink from a cup. Even when you try to give small sips, it is still more and different than what he gets with a sippy lid. The water goes down so quickly before your lo can get a good swallow. But don't worry too much about the cough....it's a protective mechanism. The term "choke" is only really used when the airway is blocked. Water can't do that, but it can penetrate to the vocal cords which causes lo (or any of us for that matter) to cough. The cough is protective and protects water from going any further to the lungs. Even if water did go to the lungs it is not harmful unless the mouth is full of bacteria.
Anyway, more info than you probably needed (I do swallowing assessments for a living). Just don't worry, they can't "choke" on water.
shannon
Just a side note, our lo's can cough just from their own saliva.we see this if lo is teeting/salivating a lot and the saliva is slipping back down the throat. Again, the cough is protective. They feel the tickle on their vocal cords.