Locate a source for watercress in your area. Since it needs flowing water to grow, finding it in the wild may be easier than trying to establish a habitat for it in your yard or garden.
Use sharp scissors or a knife to cut the stems of the watercress. Dull scissors or knives will tug on the plant's roots, disturbing them so that the plant may die. Only harvest a few leaves from each plant, which helps the plants continue to grow and thrive.
Place the watercress in a container or bag. When you get ready to use the watercress, rinse it thoroughly and cut off the stem above where you originally cut it to verify that any water-borne pathogens in the water near the bottom of the stem are removed. When you cut watercress to add it to salads or to use as a seasoning in food, place it on a cutting board and use a rocking motion with your knife so that you do not bruise the leaves.