An auxiliary drain pan for catching liquid that leaks or overflows from an appliance, system or machinery includes a central well and a pan plate surrounding the central well. The pan plate has a top surface that is sloped downwardly towards the central well such that, when the drain pan is operatively positioned on a generally horizontal plane, liquid on the top surface flows into the confined area of the well, thereby minimizing the weight of liquid collected in the drain pan. The well includes a drain line connection port and a removable wall segment for optional attachment of a water detection device. Parallel score lines in the pan plate, extending both longitudinally and transversely on all sides, define removable areas for adjustment of the overall size and shape of the drain pan, thereby allowing for customized sizing at the installation site.