What is dog water?

There are two possible answers to this. First, "dog water" may be "water intended to be used as a drinking source for a dog". This is simply potable drinking water that is set out, generally in a designated bowl or bucket, for a dog to have access to and drink from. Second, "dog water" may be a euphemism for "dog urine", in which cause it is simply the liquid waste excreted from a dog during urination.