A method for purging a reductant supply system for an engine is provided. The reductant supply system includes a reservoir to store a reductant. The reductant supply system further includes an injector to inject reductant in an exhaust conduit of the engine. The reductant supply system also includes a conduit coupled between the reservoir and the injector to supply the reductant. The method for purging the reductant supply system includes initiating purging of the injector and the conduit such that the reductant in the injector and conduit flows to the reservoir. The method further includes monitoring of the dilution of the reductant during purging and indicating a completion of the purging when the dilution of the reductant in the reservoir reaches a threshold value.