Setback distances of wellhead and catchments from septic tanks are establised by three aproaches: methods based on fixed setback distances or fixed travel times; methods based on vulnerability analysis and methods based on infection risk. In Costa Rica, the determination of setback distances is based on fixed travel times. This approach considers that during and specified travel time all microorganisms will be inactivated, and that the distance traveled during this time defines the minimum safe separation. In this approach a unitary hydraulic gradient and saturated hydraulic conductivity are considered for transport in the unsaturated zone and the natural hydraulic gradient and saturated conductivity for transport in the saturated zone. Only advection is considered as the responsible mechanism for virus transport. A new procedure is presented in this document to define the setback distance. This procedure is based on the infection risk approach. According to this approach the minimum required setback distance is defined as the distance between the injection point and the location where the contaminant reaches a maximum allowable concentration. This procedure was implemented in a computer code that considers variable saturated water flow, fractured-porous media, advection, dispersion, dynamic sorption, inactivation and mechanical filtration. A comparative analysis was performed for three hypothetical geometries using the two approaches described. The results indicate the approach normally used in Costa Rica may no reproduce adequately the possibility of catchments and wellhead contamination.