ARGH! Callum does this too! It drives me nuts. He also does the water thing AND he likes to put food in his mouth and then blow raspberries at me
If he's doing it at lunch time I usually give him 3 chances to eat (I only give him 3 or 4 bite sized things on the tray at once) and if he just throws/spits it all out then I clean up and get him out of the chair and that's it. He usually eats really well at afternoon tea and/or tea time
If it's tea time when he's being a pest then same routine but if he didn't eat much at lunch time then I will usually give him fruit/yoghurt. He oftens spits that out too so then tea time is over! If he really didn't eat much I might try again 30 mins later if he's not over tired.