In a large bowl, beat together the sweetened condensed milk and 1 ½ cups ice cold water 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.
In a large bowl, whip the 3 cups heavy cream until stiff peaks form.
Gently fold the whipped cream into the pudding mixture until no streaks of pudding remain.
To assemble dessert, arrange ⅓ of the Nilla wafers covering the bottom, overlapping if necessary.
Next, layer ⅓ of the bananas, and ⅓ 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.
