The risk characterization method employed by US EPA to quantitatively characterize the benefits of the Groundwater Rule (GWR) for drinking water computes person-to-person transmission intensity as the product of the number of primary illnesses and a static secondary morbidity factor. A population level infectious disease health effects model is used here to evaluate the implications of secondary transmission on exposures to viruses that are relevant to the GWR. These implications are evaluated via a hypothetical case study in which it is assumed that a tour group from a large population centre visits an outlying area that is served by a non-community water system with untreated or inadequately treated groundwater that is contaminated with a highly infectious virus. It is assumed that some of the exposed individuals become infected and then return home. Numerical simulations are used to estimate the subsequent number of additional infections and illnesses due to secondary transmission within the large community. The results indicate that secondary transmission could substantially impact the predicted benefits of the GWR depending on the suite of population dynamic elements and assumptions employed.