Refers to a host that shed the faeces which is causing faecal pollution in water. Depending on the specificity of an MST method, a faecal source might refer to a general group of host (e.g., all humans, all animals, or a group of animals such as canines, birds, rodents, or ruminant animals), a type of faecal waste (municipal sewage, agricultural sewage, residential septage, or an individual faeces), or a specific host animal species (e.g. human, cattle, dogs, ducks,etc.). Sometimes ambigously used for of point source of pollution (e.g. Sewage effluent pipe).