In areas of freshwater shortage water of marginal quality can substitute freshwater and be used as irrigation water, provided particular conditions are met and appropriate practises are applied. IMWI (2010) estimates "that more than 4-6 million hecaters (ha) are irrigated with wastewater or polluted water."
The prerequisite for safe Marginal water|use of marginal quality water is knowledge regarding the quality of water and the effects of dangerous components. Bacteria can be risky for human health, salt can damage soils and affect crop growth negatively and heavy metals will contaminate soils and cause risks to plants, animals and humans.
Water contains salts. When used for irrigation these salts are added to the soil. Under arid conditions, where the evaporation of soil water is higher than the precipitation, these salts raise to the soil surface by capillary rise. The accumulated salts destroy the soil structure and prevent plant growth because plants cannot take-up water due to the high hygroscopic pressure in the root zone. Drainage and appropriate agronomic practises can mitigate the adverse effects of saline water and enable cultivation of crops.
From 1997 until 2003, GTZ implemented the project “Brackish Water Irrigation in the Jordan Valley“ in Jordan. Brackish water is water of relatively moderate salt content. An important output was “Guidelines for Brackish Water Irrigation in the Jordan Valley“. The general part as well as the crops related guidelines apply also for areas outside the Jordan Valley or can at least serve as orientation.
Water used by humans is polluted and has adverse effects when reused. Reclaimed water is a synonym for treated wastewater and increasingly used among professionals because it emphasizes the aspect of restoring the water (more or less, depending on the treatment) to the previous state and make it again available to human use. The treatment method and the expenses spent determine the quality of the product. For instance, in Singapore the quality is that of drinking water (and is called New Water). Also in the USA or Israel, the standards are extremely high. However, not all countries can afford such high treatment standards and they are not needed when used for irrigation, depending on the practises applied.
The World Health Organisation (WHO) has developed appropriate guidelines which are available in ‘WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater, Volume ii, Wastewater Use in Agriculture’.
From 2004, GTZ has implemented the project “Reclaimed Water Irrigation“, also in the Jordan Valley. The guidelines elaborated in the context of the Reclaimed Water Project are available in "Guidelines for Reclaimed Water Irrigation in the Jordan Valley".
Especially farmers in cities or close to cities as well as industrial sites have to deal with polluted water. This can result in health problems, particularly if vegetables or fruits are eaten raw. Irrigation practices to reduce health risks are displayed here: IWMI (2012). Safer Irrigation Practices.pdf
IWMI (2012). Safer Irrigation Practices.pdf
IWMI (2011). Reducing Health Risks Polluted Water West Africa.pdf
Improving food safety in Africa where vegetables are irrigated with polluted water
Good farming practices to reduce vegetable contamination
- ↑ IMWI (2010): Wastewater irrigation and health. Assessing and mitigating risk in low-income countries. http://www.iwmi.cgiar.org/Publications/books/pdf/Wastewater_irrigation_and_Health_book.pdffckLR[accessed 19 April 2013]
- ↑ FAO (1994): Water Quality for Agriculture. http://www.fao.org/docrep/003/T0234E/T0234E00.htm#TOCfckLR[accessed 19 April 2013]
- ↑ WHO (2006): WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater. Volume ii, Wastewater Use in Agriculture. http://www.who.int/water_sanitation_health/wastewater/wwuvol2intro.pdffckLR[accessed 19 April 2013]