There are many activities of mankind that produce waste water or water that is mixed with organic or inorganic wastes of some kind. Hydroponics offers an opportunity to clean water that has organic wastes in it.

Aquaculture, or the raising of fish and aquatic animals, requires replenishment of water to provide clean water for the fish. Usually clean water is pumped into the fish tank and the "dirty" water with fish wastes is dumped out of the fish pond. The "dirty" water is usually loaded with organic material, mostly fish wastes, and it makes an excellent organic hydroponic nutrient.

The waste water from aquaculture is usually a mixture of ammonia, salts, and solid fish wastes. The ammonia and salts can be used directly by the plants, but the fish solids have to be broken down by microbes. So the hydroponic grower should have an active culture of microbes in the media to break down fish solids so the plants can use them. The best media for microbe cultures is grow rock or pea gravel.