Mix: In a large bowl, whisk together the condensed milk, cold water, milk and vanilla until smooth. Whisk in the pudding mixes. Refrigerate for at least 30 minutes.
Fold: Take the pudding out of the refrigerator. Fold in the cool whip, until everything is mixed smoothly.
First Layer: Place a single layer of vanilla wafers (around 30) on the bottom of a deep 13x9 aluminum pan. Add a single layer of banana slices. Spoon on half of the pudding and spread it out.
Second Layer: Add another single layer of wafers on top of the pudding. Add another single layer of banana slices on top of that. Spread on the remaining pudding mix. You may have a little leftover.
Chill: For best results, refrigerate at least 30 minutes before serving.
Serve: Just before serving, sprinkle the top with some crushed vanilla wafers.
Notes
To reduce the sugar content, you can use the 1-ounce boxes of zero sugar pudding mix. Instead of Cool Whip, you can use 6 cups of homemade whipped cream. Just whip 3 cups of heavy cream into stiff peaks and fold in 1/4 cup powdered sugar.