New Zealand dairy farms generate about 70 M m³ of liquid dairy parlour effluent annually. Local Government encourages land application of this effluent; generally applied by overhead sprinkler. However, increasing microbial pollution of waterways is being reported. We investigated the transport of faecal coliforms and a host-specific Salmonella bacteriophage through eleven soils following application to large intact barrel lysimeters (460 mm dia. × 520–700 mm high). Effluent was generally applied at a rate of 5 mm h^-1 followed by about 1 pore volume of simulated rainfall applied continuously at 5 mm h^-1. The resulting microbial breakthrough curves were rated as having either a high, medium or low potential for microbial bypass flow; depending on the position of the peak microbial concentration in the leachate relative to the drainage volume. Soils in which the leachate microbial concentration started at its peak concentration then declined were rated as having a high potential. If the concentration rose to a peak within 25-mm of drainage the soils were rated as having a medium potential. Insights gained from the microbial breakthrough curves were related to soil properties such as soil structure, coatings on peds and the nature of the parent material. The soil properties were then matched to criteria used to define New Zealand Soil Classification (NZSC) classes or their accessory properties. Finally, all NZSC classes were rated for potential microbial bypass flow allowing a 1:50 000 scale map of all New Zealand soils to be generated using a GIS and the spatial digital soil database.