Existing theory is used to decribe the underground movement of renovated wastewater. Equations are presented to predict the minimum underground detention time for ground-water recharge systems. Analysis of the flow in a deep aquifer system showed that a nitrate peak, associated with the newly infiltrated wastewater, would be considerably flattened by the time the renovated water reaches the collection well. In shallow aquifers, the degree of attenuation is much less and a distinct nitrate peak would show up at the collection drain.