In a large mixing bowl, whisk together cold water and sweetened condensed milk until combined.
Add the instant vanilla pudding mix and whisk for about 2 minutes until fully blended.
Cover the bowl and refrigerate for at least 4 hours, or overnight if possible.
In a medium mixing bowl, whip the heavy cream until stiff peaks form.
Gently fold the whipped cream into the chilled pudding mixture until well combined.
In a 9x13 inch baking dish or trifle bowl, layer one-third of the Nilla wafers.
Add a layer of one-third of the sliced bananas over the wafers.
Spread one-third of the pudding mixture over the bananas.
Repeat the layering process two more times, ending with the pudding mixture on top.
Cover the dish and refrigerate for at least 4 hours before serving.
Notes
For the best flavor, allow the banana pudding to sit overnight in the refrigerator so the flavors can meld together. When serving, consider garnishing with additional Nilla wafers or banana slices for added presentation.