Brown ground beef and onion in a medium skillet; drain and set aside. In a two quart saucepan, combine cheese soup, water, chili and enchilada sauce, mixing well. Add meat mixture to saucepan, combine and heat thoroughly.
Cut the tortilla shells in half and line the bottom of a buttered 9X13 glass pan with 12 halves. Pour half the meat mixture over the shells. Sprinkle half the shredded cheese over the meat mixture. Place the remaining 12 tortilla shell halves on top of the cheese, add the remaining meat mixture and top with the remaining cheese. Bake, uncovered at 375 degrees for 20 minutes.