I have to admit I read this with some growing alarm fir the cat! I understand completely your concern for the dog but the cat has been there for 10 long years and this is his safe territory and home. Unless you introduce dogs and cats carefully, slowly and cautiously - and follow all those guidelines (there are many wonderful articles online, simple google "introduction of dog and cat" of some varaiation thereof and select one. I believe there is one on this very site if you browse for it.
It is not the cat's fault and cats never respond to punishment. In fact, it makes them fearful and this could even result in more aggression. For some reason, this kitty feels threatened. And your dog needs help in understanding how to live with a cat as the newcomer.
Lucky's suggestions are great - give him his own bowls. Even with two cats, seperate bowls are a wise idea. I have three cats at the moment and they each have their seperate bowls - though they will sometimes share water but that is their choice.
PLEASE never spray the cat with water - that is cruel and unecessary and the cat will not know why you are doing it and only fear you.
Good luck with this - I hope your dog becomes happier and the two become good friends. It sometimes can take time and even intra species relationships that began badly can do well if you start from scratch after introducing them properly.
"There are two means of refuge from the miseries of life: music and cats" Albert Schweitzer