When purchasing watercress in the store look for fresh green leaves; yellowing or wilting are signs of age. Watercress does not have an extended shelf life, so it should be used within a few days of purchase. To get maximum life out of the plant remove the rubber band, separate the bunch and wash it. After is has drained put the loose cress in a Ziploc bag and remove all the air with a straw. Keep it sealed and only remove the amount that you will be using at that moment and place it back into the refrigerator instantly. This method will keep your watercress fresh for up to three days.