Before beginning, place your mixing bowl and mixer beaters (or whisk attachment) in the freezer for 15-30 minutes. It is very helpful to have a cold bowl and beaters to achieve extra creamy texture.
In a small bowl, whisk together the cold water and the gelatin. Let sit for 2 minutes. It will begin to take on a gelatin consistency. Then, heat in the microwave for 10-15 seconds to warm and bring back to a liquid consistency. Set aside to cool!
To the chilled mixing bowl, add the cream, sugar/sugar substitute, and vanilla. Mix on low speed until the mixture becomes frothy and small bubbles begin to form. While mixture is still running, gradually add the gelatin mixture a few spoonfuls at a time. Once all the gelatin has been added, increase the speed to medium-high.
Mix on medium-high until the cream begins to visibly thicken, about 3-4 minutes. You'll know the Cool Whip is done mixing when the mixer stops and stiff peaks will hold their shape.