With the water spinach still bunched, trim away the lower 1-2 inches of the stalks, unless it is very young and tender. Cut the water spinach into 3 inch lengths, including the stems.
Soak the vegetables in a large basin of cold water to remove sand and dirt. Change the water 3 times, being sure to lift the vegetables out of the water each time to avoid agitating the grit that’s settled at the bottom of the basin. Drain thoroughly, shaking off any excess water.