The role of water in the development of a post-depositional magnetisation in Chinese loess was investigated in a series of laboratory experiments. Both wetted and dry dissagregated loess samples developed a magnetisation related to the applied magnetic field. It was possible to distinguish between an unstable viscous magnetisation in the dry samples and a stable component developed in the wetted samples. This can be attributed to magnetic grain re-alignment in water-filled pore spaces. In the natural environment this process can occur during seasonal saturation of the top-most loess layer, giving rise to a zone of detrital PDRM development that migrates upwards with loess accumulation, producing a continuous record of geomagnetic field behaviour.