Add the water to a small pot on your stove, sprinkle the gelatin over the water and stir over a low heat until completely melted. About 1-2 Minutes. Allow to cool completely.
Add the pumpkin puree, condensed milk and pumpkin pie spice to a medium mixing bowl and beat until well mixed, about 1 minute.
Set aside ½ cup of the whipped topping and spoon the rest into the pumpkin mixture and lightly fold in the cool whip.
Add the cooled gelatin mixture and stir again. Then, pour the pumpkin pie filling into the store-bought crust.
Place into the refrigerator for 4 hours or more, or pop in the freezer until completely set.
Use the remaining ½ cup whipped topping to serve the pie with. Add a dollop (or pipe it) right when serving and dust with a little pumpkin pie spice.