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Black water is the term used to describe raw sewage. Black water is a pollutant containing nutrients, metals, toxins and pathogens that can have a detrimental effect on natural ecosystems and wildlife, as well as risks to human health. Sewage can spread gastroenteritis and also contains phosphorous and nitrogen which increase levels of algae and reduces water quality. Chemicals such as chlorine, formaldehyde, ammonium and zinc compounds, used to disinfect breakdown and deodorise waste, are toxic to marine life.


Clubs and training centres play an important role in educating the boating community on the issues of black water and in promoting best practice.


One flush on a boat contains the same amount of bacteria as 250,000 flushes through the sewage treatment process.


Sewage discharge is prohibited by law on most inland waterways and as part of coastal and estuarine bylaws or marina policies. The Environment Agency has overarching powers of regulation.


Regulations for the prevention of pollution by sewage into the sea are contained in Annex IV of MARPOL. These regulations apply to ships of 400 gross tonnage and above engaged in international voyages or ships which are certified to carry more than 15 persons.


Although no specific provisions are made for smaller pleasure vessels, it is important to consider the impact of discharging raw sewage from a sea toilet or holding tank into the sea. It is best practice to return all waste generated on board to shore waste reception facilities where possible.


If a holding tank is fitted it should be used and only emptied at either a pump out station or when more than 3 miles offshore. This is because in the open sea waste will be quickly diluted and dispersed by wave action and currents. On vessels without a holding tank avoid the use of toilets in poor tidal flushing areas (e.g. estuaries, inland waterways, inlets and crowded anchorages) and use marina or shore facilities where possible.


As a club and centre you can help by:


  • Providing your own facilities such as a pump-out facility and/or accessible on-shore toilets, with recycled toilet paper.
  • Promoting facilities near your location such as a nearby pump-out facilities:
    • Use and promote The Green Blue’s Pump Out Directory.
    • Encourage your local marina to install a pump out facility.
  • Raise awareness of the issues relating to black water and promote good practice:
    • Encourage members and students to use marina and shore side facilities whenever possible.
    • The use of environmentally friendly low phosphate cleaning products on board.
    • Use of recycled toilet paper which breaks down easier than standard paper.

Coastal Boat User Guidance:

  • Use holding tanks or a portable toilet if you regularly sail in poor tidal flushing areas such as estuaries, inlets and crowded anchorages
  • Empty holding tanks only when more than 3 miles offshore in the open sea where waste will be quickly diluted and dispersed by wave action and currents.
  • When visiting new sites give consideration to the environmental sensitivity of the area before using your sea toilet
  • Fit a holding tank in your boat, some European countries require it by law

Inland Boat User Guidance:

  • When using chemical toilets plan ahead where you will empty these as they use toxic substances that only a few pump out facilities will accept. Never empty down a drain, always dispose of into an appropriate sewage system
  • Find out the regulations of the waterways you visit before setting off

Additional Information:

Further information is available on the International Maritime Organization (IMO) and the Maritime and Coastguard Agency (MCA) websites.

The Canal and River Trust maintain a list of their own water points and pump outs, as well as a private pump out directory.

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