I have one in a seven gallon on my computer desk in my bedroom, and one in a 20 gallon between the desk and the TV. I've run out of room for tanks becuase I'm not allowed to have any throughout the house, and I like keeping bettas in large filtered and cycled tanks. (Personal choice - I think they take a lot less work this way!)
I've woken up to my room smelling like boiled cabbage, but never stinky fish water. (The snails get cooked collard greens - now I feed them in the morning before I go to work!)