Retention of disinfectant activity in the presence of hard water.

Inactivation of germicidal activity by hard water has been reported by a number of investigators (Armbruster and Ridenour, 1949; Dvorkovitz and Crocker, 1950; Mueller and Seeley, 1951; Chambers et al., 1955). Both synthetic and natural hard waters have been studied in attempts to determine more precisely the characteristics of inactivating systems. In general, it appears that the interference is a result of many factors interrelated in a complex way (Armbruster and Ridenour, 1949; Mueller and Seeley, 1951, Chambers et al., 1955; Klimek and Bailey, 1956; Meggison and Mueller, 1956). However, hardness caused by certain ions, particularly calcium, magnesium, and bicarbonate, is believed to be of greater importance than total hardness (Armbruster and Ridenour, 1949; Mueller and Seeley, 1951; Chambers et al., 1955). Most studies of this type have been concerned primarily with the deleterious effects of hard waters on the sanitizing properties of quaternary ammonium compounds. Only rarely (Dvorkovitz and Crocker, 1950) has attention been paid to other types of antimicrobial agents; phenolics have been especially neglected. Also, no attempt has been made to study possible hard water inactivation of surface disinfectants using a performance test. Recently, the Square-Diluent method was developed at this laboratory for testing disinfectants under conditions of use simulating floor disinfection (Stedman et al., 1954a, b). This technique has been used to study the efficiencies of different types of disinfectants on various inanimate surfaces (Stedman et al., 1954b, c, 1955a, b) and the physico-chemical forces involved in the disinfection of such materials (Stedman et al., 1955a). In view of the many different sources of water which are employed in preparing disinfectant solutions in practice, it was felt advisable to extend past work to include the effects of hard water upon disinfection of surfaces.