This Report presents information on the current state of knowledge of the origins, occurrence, nature and effects of sewer solids for use by engineers, scientists, administrators and water quality planners for the planning, design and operation of sewerage systems. The report addresses both sewer maintenance requirements and environmental protection issues. Increasing environmental standards, coupled with public expectations, have led to stringent water quality standards. In response to this, it has been necessary to develop new methodologies and computer based analytical techniques to model and understand the performance of all aspects of waste water systems. Fundamental to these techniques is the understanding of the way in which sewer solids contribute to the poor performance of wastewater systems and consequential environmental damage. The information presented in this Report about the origins, nature, movement, hydraulic and polluting effects of solids in sewers has enabled strategies and rules to be developed for the management of sewerage systems to minimise the deleterious effects of these solids and associated pollutants. Scientific & Technical Report No. 14