The present invention provides a quaternary ammonium etidronate compound (QAE) comprising a quaternary ammonium cation and an etidronate anion, having the Formula I. A method for the preparation of such compounds is described by reacting a quaternary ammonium salt with an etidronic acid or salt thereof. Variable ratios of each reactant may also be used to form different QAE compounds. The quaternary ammonium etidronate compounds is useful in water treatment, cosmetic, hygiene, personal care, paint, coating, wood treatment, agrochemical, antimicrobial, disinfectant, or biocidal compositions; as the compound provides high anti-corrosive and biocidal properties; and low scaling properties. A water treatment composition is also described, having a QAE compound of Formula I and a water treating biocidal agent, useful in cooling towers and other recirculating water, or recreational water system.