Heat taco shells as directed on box.
In 10-inch nonstick skillet, cook beef over medium-high heat 5 to 7 minutes, stirring frequently, until thoroughly cooked; drain. Stir in water and taco seasoning mix; heat to boiling. Reduce heat; simmer uncovered 3 to 4 minutes, stirring frequently, until thickened.
Spoon beef into taco shells.
