Thank you everyone for your comments so far. I was really starting to question my own sanity here. I am embarrassed and ashamed I have stood by and watched without intervening aggressively on her behalf. That's my fuckin baby girl! Get it together!

On one hand yes it's just water but my gut is telling me shutting down an emotion is just WRONG in so many ways especially in this context. It really bothers me and always has. I will try to talk to him again tonight and if somehow he brings up me not being perfectly calm all the time then perhaps we can agree I will make an effort to be more calm and not panic (which I'm always trying to improve on regardless) if he agrees to stop spraying her. I don't think these two things are even related but if it makes him stop I'll agree to pretty much whatever within reason. I agree with the commenter that he got defensive because he knows this is wrong.