Black water is water flushed from toilets.
In a land-based habitation this can be dealt with using reed bed filtration.
On a boat typical solutions are to use a holding tank or to simply pump it over the side (see RYA information page) but another way to reduce the problem of dealing with black water is to eliminate it completely, for example in a composting toilet such as the Envirolet
Envirolet® uses little or no water and does not burn, use chemicals or require a septic tank.
• North American made since 1977. Certified to meet ANSI/NSF Standard-41.
• Lifetime Warranty on body, 5-Years on everything inside.
• All Envirolet® Systems feature Automatic Six-Way Aeration™.