Mix sweetened condensed milk and cold water on medium speed for 1 minute. Add pudding mix and mix until pudding is smooth about 2 minutes. Cover and refrigerate for 3-4 hours, or overnight.
In a clean bowl, whip the heavy cream on medium speed for about a minute, then increase speed to med-high and whip until stiff peaks form, about 1-2 more minutes, do not to over whip.
Combine the whipped cream with the pudding mixture. I personally like to fold in the whipped cream using a spoon so the mixture keeps the fluffy texture.
Spread a layer of cookies on the bottom, layer with pudding and then bananas Top with more pudding and a wafer. Continue until your parfait glass is full.
Cover the top layer with crushed nilla wafers and banana slices. Enjoy!