Abstract: An improved electrostatic water treatment apparatus is described which can operate for long periods without failure in very harsh environments, such as extreme and rapid temperature variations. It includes an elongated, cylindrical electrode having end closure cap members. At least one of these end caps has cylindrical side walls with an inner portion thereof telescoping within the cylindrical electrode and an outer shoulder portion extending axially outwardly beyond the end of the electrode. A continuous coating of silicone adhesive is provided over the exterior of the electrode and the outwardly extending shoulder portion of the end cap. A thin, impervious insulating sleeve then overlies the silicone adhesive coating, covering the exterior of the electrode and the outwardly extending shoulder portion of the end cap.