Mound filter systems are used to treat wastewater from structures not served by public sewer. This guide describes mound filters which deal with domestic wastewater after primary treatment (settlement) and after secondary treatment (aerobic or anaerobic biological treatment). It draws on work from around the world, including the UK. The filtration system was developed from the 'NODAK' system which was first used in North Dakota in the twentieth century; more recently it was developed into the Wisconsin mound sytem. The design guidance covers the most common types of mound filters that are likely to be employed in the UK in the near future. The guide includes an introduction to wastewater treatment, guidelines on construction and maintenance of mound filters, design criteria, and trouble-shooting solutions. 60 pages.