We prepared soup stock samples from bonito and kombu, niboshi and kombu, beef and vegetable and chicken with mineral water of differing hardness. The mineral content of each was measured (distilled water, 0 mg/l ; soft water, 28 mg/l ; hard water, 303 mg/l ; and very hard water, 1,427 mg/l ), and sensory tests were conducted to evaluate the effect on stock taste of the mineral water hardness. The soup stock samples of bonito and kombu and niboshi and kombu had comparable palatability between hard water and soft water, but very hard water resulted in low preference. The calcium content of the soup stock from bonito and kombu and from niboshi and kombu prepared with hard water was 2-3 times higher than that of the equivalent soup stock prepared with soft water. Using hard water to prepare soup stock that is often used in Japanese food appears promising as a method of calcium supplementation. The palatability of beef and vegetable soup stock was most favorable when made with hard water, the calcium content of this stock prepared with hard water being 1.9 times higher than that of beef and vegetable soup stock made with soft water. Unlike the other samples of soup stock, the chicken stock prepared with very hard water was assessed as moderately palatable. Since its calcium content is more than 10 times that of soft water, very hard water has proven value in soups and one-pot dishes.