To produce food, water is consumed by the plants in the field through evaporation and transpiration. The amount of water needed varies with crops and depends from place to place, on local productivity and conditions of available water supply through rainfall or irrigation. Once the product is harvested and becomes available on the market, the water embedded in the product changes status from 'real' water to 'virtual' water. See how much water is needed to produce: 1 potato, 1 slice of bread, 1 apple, 1 egg, 1 glass of milk, 1 hamburger