37 building, installation and maintenance of water treatment installations, namely, waste water treatment units comprising of aerator treatment tanks, sludge lagoons, screw pumps, sludge presses, grit screens, sludge driers, pumps, control systems, sludge disposal systems and ancillaries, and wateraparatus, namely, screens, raw water pumps, treated water pumps, surge controls, pipelines, aerators, closing equipment, rapid gravity filters, disinfection equipment, motor control centers, program logic controllers, instrumentation, consulting services in the field of installation, building and reparation of water supply and water treatment installations