Abstract: A method for monitoring water quality including deriving calcium hardness and M alkalinity from the linear functional relation between calcium hardness and specific conductivity, and that between log value of M alkalinity and pH value, simplifying the temperature curve into a formula, and calculating directly the saturation index. A multipurpose and inexpensive automatic water quality monitoring apparatus that can be adapted for use in cooling towers, swimming pools, and boilers may be made from a combination of an conductivity meter, pH meter, and oxidation reduction potential meter commonly used in testing, and a simple algorithm of a central processing unit.