To Discard Soak Water or Not Some people are more susceptible than others to the discomforts of the gas, or flatulence, sometimes caused by eating beans. Flatulence occurs when bacteria normally found in the digestive tract reacts on certain chemical compounds in beans. Some are water-soluble and will be partially removed when the bean soak water is discarded. Small amounts of water-soluble vitamins and minerals are also removed by discarding the soak water. Therefore, many cooks believe it is nutritionally important to use the soak water for cooking the beans.
Current research shows that only small amounts of nutrients are lost.
For many people, the discomfort avoided by discarding the soak water is more important than the small amount of nutritional benefits from using it. If you consistently have problems cooking beans to the desired tenderness within the specified cooking times, it is possible you have hard water. Another sign of hard water is the appearance of a thick white or gray residue on the inside of your teakettle every time you boil water. This is caused by the presence of excessive amounts of certain minerals. High concentrations of these minerals interfere with chemical and physical changes that are supposed to occur in beans during soaking and cooking.