How to conserve household gas. Use as little water as possible when cooking most vegetables. For in addition to conserving their vitamin content, this method decreases cooking time and uses less gas. The best way to cook many vegetables is to bring the water to a quick boil, then reduce the flame when the boiling has started. A high flame will not hasten the cooking. All that is necessary is to use a low blue flame sufficient to keep water boiling. Sourced from the Library of Congress.