The water displacement method for sous vide is one of two options for bagging when sous vide cooking. You need to ensure all of the air is out of the plastic bags containing food when using sous vide. One option is to use a vacuum sealer, the other is to use the water displacement method. For the displacement method, you: 1. Bag the food in a freezer grade Ziploc or Stasher bag 2. Seal bag most of the way, leaving roughly 2" open 3. Submerge the bag into a container of water so that the unsealed portion is just above the water line. Then seal the unsealed portion.