dump the oil and filter, then dump another whole quart in with the drain plug out still, this will hope fully flush out any water in the pan still. then fill your filter with oil, put the plug back in, and dump the rest of the oil in. run it for a bit, then check the oil, if the oil is foamy or milk shake colored change it again.
depending on the year of your car, and where the drain plug is, if its on the side, some water maybe left in. drain plug on the bottom of the pan less likely to hold water.
is this the car in your avatar? or a newer GP?
