Gives guidance on the: - selection of wastewater treatment plants to treat domestic wastewater for applications for populations up to 50 PE in areas without a public sewer; - minimum performance required for wastewater treatment plants that have been tested to I.S. EN 12566 (Parts 1, 3, 4 and 6) standards & - scaling parameters and the sludge storage capacity necessary to achieve the minimum performance recommended for wastewater treatment plants that have been scaled up from the tested plant.