Sanitary District No. 5 of Marin County provides collection and treatment of wastewater to parts of the Tiburon Peninsula and the City of Belvedere. The District serves over 3,500 households and has been servicing the area since the early 1940s. The District collects, processes, and treats wastewater in accordance with State and Federal Regulations under an NPDES (National Pollution Discharge Elimination System) Permit that regulates sanitary agencies.

The District is an independent local agency governed by an elected Board of Directors, who are all residents of the District.

A District Manager, appointed by the Board, runs the day-to-day operations of the District and advises the Board.