The aim of the current study was to calculate the size of protection zones around (sub)oxic and anoxic sandy aquifers without confining layers using a virus infection and transport model. The maximum allowable virus infection risk was 10(-4)/person/year at the 95% confidence level. Model results demonstrated that phreatic (sub)oxic sandy aquifers in The Netherlands required protection areas with a residence time of 43-117 d to ensure that the maximum virus infection risk would not be exceeded. This was 0.7-2 x the current guideline of 60d. In contrast, phreatic anoxic sandy aquifers without confining layers needed protection zones of 555-898d to stay below the maximum virus infection risk, 9.5-15 x the current guideline. A sensitivity analysis of the model demonstrated that the calculated protection zone was most sensitive for virus inactivation rate and collision efficiency. Values of both parameters were predicted from values obtained from previously published field and laboratory studies. At present, as it is unknown if these values can also be used at other locations, model results should be interpreted with care.