Beat the condensed milk and water till smooth. Add the pudding mix and beat again until smooth. Cover and refrigerate till firm, at least 1 hour and up to overnight.
Beat the cream till stiff peaks form, being careful not to overbeat. Add the chilled pudding mixture, a spoonful at a time, beating on low speed after each addition.
In a large bowl, pan or container spoon one-fourth of the pudding over the bottom, spreading into an even layer. Top with a layer of Nilla wafers followed by a layer of sliced bananas. Repeat layering, finishing with the pudding mixture. Top with Nilla wafers if desired.
Cover and refrigerate for 4 - 6 hours, so that the wafers absorb the pudding mixture and soften. Serve immediately or keep refrigerated for up to 8 hours.
