Scrub the potatoes and cut in half lengthwise. Prick the potato skin in several places with a fork. Place the cut sides down on a microwavable plate, leaving room around each potato. Cover with microwavable plastic wrap, venting one edge. Microwave the potatoes on High for 4 minutes. Carefully uncover and turn the potatoes over. Re-cover the potatoes and microwave again for 4 to 6 minutes or until soft. Meanwhile, cook the ground beef in a medium skillet over medium-high heat until no longer pink; drain. Stir the taco seasoning and water into the beef; cook until thick. When the potatoes are cooked, using hot pads to protect the hands, scoop the flesh from the potatoes, leaving a ¼-inch shell around edges. Chop the potato flesh and add to the meat mixture. Add 1/4 cup of the sour cream to the meat and potato mixture. Spoon a heaping 1/2 cup of meat mixture into each potato shell. Top with cheese, green onions and a dollop of the remaining sour cream.