Abstract: A method and apparatus for combining multiple sources of intake water for use in hydraulic fracturing and other oil and gas drilling operations and treating the water with peracetic acid prior to discharging into one or more frac tanks or into a well. The apparatus includes a manifold assembly that combines water from multiple sources prior to entering a mixer where PAA is injected in a finely dispersed spray under pressure to thoroughly mix the PAA and intake water prior to be discharged into one or more frac tanks. By using a manifold assembly, the apparatus is easily transported to different job site-locations and permits the use of standard connection fittings to easily connect the apparatus to existing fracturing equipment. A method for injecting the PAA and testing and adjusting the level of PAA is also disclosed.