By definition, when pH Actual = pH Saturation, the LSI is zero. However, in special cases where these terms are greater than 6.5, an alternative index, the RSI, predicts CaCO3 dissolution. Conversely, when the terms are equal but less than 6.5, the RSI predicts CaCO3 deposition. Furthermore, when there is virtually no calcium but ample alkalinity present, both conventional indices predict scaling when in fact none will occur. A new index is proposed that predicts not only scaling tendency but the amount of CaCO3 precipitation. The precipitation is always proportional to the water's alkalinity, calcium, TDS and temperature.