At home where the bowl gets washed and refreshed frequently my pups usually share unless they are attached to their own bowl. However, "out" is a different story. I am really careful about dogs drinking from a communal bowl at a park - I don't want to risk them ingesting a parasite even though that is more likely to come from eating something they shouldn't! Also around communal bowls and taps there's often stagnant water that pools which I try and keep my doggie charges away from in case of the dreaded giardia (which is going around my neighborhood and is not fun to deal with!)