Starting from the famous Ross-Macdonald epidemic model which describes the infection dynamics of malaria for a collection of isolated patches, we construct a coupled multi-patch infection model. The coupling is caused by the fact that humans move between patches, and hence can pick up the infection in one patch and later introduce it in another patch. A central question in this context is how sources and sinks can be distinguished from one another. An isolated patch is called a sink (source) if its corresponding basic reproduction number is less (larger) than 1. This implies that in case of a sink (source) the infection dies out (persists) provided that the patch would be isolated. We shall see which epidemiological parameters, combined with the measurements of proportions of infectious humans within all patches are needed to determine the sinks and sources. Implications on control of the malaria infection throughout the network of patches will be discussed as well.