Black water on board: definition, impact and good practices
When you're sailing, it's essential to think about the environmental impact of your boat. Among the sources of pollution that need to be controlled, black water - i.e. waste water from toilets - is a real issue. Discharging it directly into the sea can have harmful consequences for water quality and marine biodiversity. Fortunately, there are solutions for managing this water responsibly and limiting its impact. Here are the best practices and equipment for environmentally-friendly sailing. 🌊💙
What is balck water?
There is a difference between grey water and black water. Grey water is washing water discharged from sinks, washbasins, showers, etc.
Black water is water from toilets. Unfortunately, it is often discharged untreated into the sea.
Two things make it harmful to the environment and biodiversity:
- pharmaceutical residues from medicines,
- chemical additive residues, which are also found in black water.
In addition, large concentrations of black water can sometimes be found in harbours or mooring areas. However, it is forbidden to discharge wastewater in harbours and in the 3 nautical mile zone.
The impact of black water on the environment
Like grey water, black water is harmful to the environment because it:
- presents health risks: when this water is discharged near bathing areas, the bacteria it contains can cause illness.
- disrupt ecosystems: in high concentrations, black water significantly accelerates the development of aquatic vegetation and the depletion of oxygen in the environment.
- threaten marine life: pharmaceutical residues and chemical additives have serious consequences for marine animals. For example, they can change the sex of certain living organisms.
Good practices on board and in the harbour
It is essential to reduce the impact of our activities on the environment. To do this, we can adopt simple ecogestures.
- Use the harbour toilets

By using the toilets in the harbour rather than those on your boat, you can reduce the amount of waste water discharged into the sea. It's a simple gesture that helps to preserve water quality and protect marine fauna.
It's also a more practical and comfortable solution, avoiding the time-consuming management of black water tanks on board.
Preserving the ocean starts with small, everyday choices! 💙🚤
- Use the black water pumps
Brest's marinas are equipped with black water pumps to prevent emptying at sea or on the pontoon.
If necessary, harbour agents can help you use these pumps.

Managing black water correctly means taking action to preserve the sea and biodiversity. By adopting good practices and using the right equipment, every yachtsman can help limit pollution. A small effort for a big impact on the environment! 🌿⚓