Mix together the water, pudding mix, and sweetened condensed milk until smooth. Make sure there are no lumps! Refrigerate for at least 4 hours, or overnight until it sets up.
Whip the heavy cream until soft peaks form. Working in thirds, fold the whipped cream into the pudding mixture until well combined.
In a trifle bowl, layer the vanilla wafers, sliced bananas, and pudding mixture. Continue until you use all the pudding mixture! Refrigerate for at least another 30 minutes before serving. Enjoy!