Boiling often results in a considerable loss of nutritional value, as many vitamins are lost if the cooking water is discarded. Vegetables cooked for only a few minutes will retain more vitamins than vegetables boiled for longer. It takes no more time to steam vegetables, and this method retains more of their nutritional goodness and flavor.
The best equipment for steaming is a bamboo or metal steamer, or a collapsible steamer that can be put inside a saucepan. Bring the water to a rolling boil (with bubbles all over), and then add the vegetables, spread out in a single layer. The rack should be about 2.5 cm above the boiling water and the steamer should be covered with a tightly fitting lid to retain the heat.
** Asian Online Recipes