Water can leach water-soluble vitamins (B and C) out of food. The less water you use, the fewer vitamins you lose. Many leafy vegetables, including spinach, need no water because the moisture that clings to the leaves after you have washed them is ample for the first minute of cooking. As the leaves cook, they contribute enough water of their own for the pot. However, cooking in a generous pot of water is called for when you want to reduce the strong flavors of some vegetables.
** Asian Recipes