Abstract: An apparatus and method is disclosed for treating a liquid with a first and a second chemical. A liquid to be treated flows into a first inlet port of an intake manifold. A second inlet port of the intake manifold introduces a first chemical into the liquid. A first static mixing device comprising a spirally twisted tube forming a plurality of helixes and having an inlet port connected in fluid communication with an outlet port of the intake manifold is provided for mixing the first chemical with the liquid. The outlet port of the first static mixing device is connected to a first inlet port of an interconnecting manifold. A second inlet port of the interconnecting manifold introduces a second chemical into the liquid. A second static mixing device has an inlet in fluid communication with an outlet port of the interconnecting manifold for mixing the second chemical with the liquid and for eluting the treated liquid from an outlet port of the second static mixing device.