The purpose of water sanitation is to transform water that has been polluted by human activity (domestic, agricultural, industrial) into water that can be assimilated into the natural environment. There are numerous water sanitation solutions from the collective level that exist as individual solutions, referred to as "autonomous." All of these are based on bacteriological activity to clean up contaminated water. Likewise, each system, at its output, returns the water to the natural environment by infiltration or by leach field. The output of this water sanitation is not potable. It is highly rich in minerals that the sun and plants may assimilate, comparable to a fertilizer. Returning it to the aquatic environment is prohibited in most cases, except when infiltration or leaching is not possible. As the aquatic environment is more sensitive than the soil, the input of nutrient-laden water involves a high risk of disrupting the natural environment, or even causing asphyxiation or eutrophication.