MARPOL Annex IV regulates the discharge of sewage into the sea; ships’ equipment and systems for the control of sewage discharge; the provision of facilities at ports and terminals for the reception of sewage; and requirements for survey and certification. It also includes a model International Sewage Pollution Prevention Certificate to be issued by national shipping administrations to ships under their jurisdiction.The annex entered into force internationally on 27 September 2003. A revised annex was adopted on 1 April 2004, and entered into force date on 1 August 2005.

The revised annex applies to new ships engaged in international voyages, of 400 gross tonnage and above or which are certified to carry more than 15 persons. Existing ships, registered to States that are party to Annex IV, have been required to comply with the provisions of the revised Annex IV since 27 September 2008.

The annex requires ships to be equipped with either a sewage treatment plant, a sewage comminuting and disinfecting system, or a sewage holding tank. The discharge of sewage into the sea will be prohibited, except when the ship has in operation an approved sewage treatment plant at a distance of more than 12 nautical miles from the nearest land.