Pour the condensed milk and water into a large mixing bowl. Using a hand mixer, beat together until well combined, about 1 minute. Add the pudding mix and beat well, about 2 minutes.
Cover and refrigerate for 3-4 hours or overnight. It is very important to allow the proper amount of time for the pudding mixture to set so it will not be watery. In a bowl of a stand mixer or a large mixing bowl if using a hand mixer, whip the heavy cream until stiff peaks form. Gently fold the whipped cream into the pudding mixture until no streaks of pudding remain.
The dessert can be made in a large glass bowl with 4-5 quart capacity (a 9x13 baking dish also works).
To assemble, arrange 1/3 of the Nilla Wafers covering the bottom, overlapping if necessary. Next, layer 1/3 of the bananas, and 1/3 of the pudding mixture.
Repeat twice more, garnishing with additional wafers or wafer crumbs on the top layer.
Cover tightly and allow to chill in the fridge for at least 4 hours or up to 8 hours.