 When the modeling phase is complete, selected systems are validated using a professional third party to provide oversight and to determine how closely the model is able to predict the reality of system performance.System validation uses non-pathogenic surrogates such as MS 2 phage or "Bacillus subtilis" to determine the Reduction Equivalent Dose (RED) ability of the reactors.Most systems are validated to deliver 40 mJ/cm2 within an envelope of flow and transmittance.