[[Image:closingUrban.png|thumb|right|200px| Part of the poster [http://www.ecosanres.org/images/Poster-ClosingTheLoop-Urban-large.jpg Closing the loop on Sanitation in Urban areas], produced by [http://www.ecosanres.org EcoSanRes].]]
Human faeces and urine contain a large amount of nutrients, which can be used in agriculture for crop irrigation, for fish aquaculture, or aquatic vegetable pond fertilization. In many cultures, for example the Chinese, the idea that 'waste is too valuable to waste' is well known, and best weight loss pills has been practiced for centuries. In many other cultures however, sanitation products are hardly used for productive use, although interest is growing.
The '''Ecological Sanitation (EcoSan)''' movement (also called 'sustainable sanitation') has led to more interest in this the sanitation field. When sanitation products are reused, great care has to be given to dealing with the potential health and environmental risks of human waste products. Large-scale sewerage-based systems have significant drawbacks. Enormous investments are needed, operating and maintenance costs are very high, the water consumption is very large, and a large volume of waste is produced which can be costly to treat. Especially in arid zones, the water use is a problem. A second problem is that in cities, all kinds of waste are disposed of in the sewer, leading to a very varied mixture which is difficult to process. Ecological sanitation can both be applied in cities (often in public toilet blocks), and in peri-urban and rural areas.
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