Abstract: Apparatus and method for practice in an over-the-road vehicle to determine whether effluent water released in an operating water treatment system (plant installation) can be adequately treated to remove contaminants so the effluent may be reused at the plant rather than discharged to the environment with inimical effect. The frame of the vehicle supporting a plurality of clean holding tanks, a plurality of functionally different water treating units, an analysis laboratory, a pilot cooling tower simulator, and a pilot boiler simulator. The effluent is transferred from one of the holding tanks to at least one of the water treating units to reduce the contaminant level. When the contaminant level has been reduced to a level appropriate for reuse at the plant, the effluent is transferred to one of the simulator apparatus for evaluation of the treated water in the corresponding plant process.