How long does a phone have to be in water before it doesn't work at all?

See, I'm trying to break my phone because I have a thingy with best buy and i can get a new phone of the same value if it's broken. My mom doesn't want me to get a new phone but i hate the phone i have and i tried drowning it in water. then she puts it in rice and it dries out and it works fine... I just want to know how long a phone has to be submerged before it doesn't work at all.