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'''To reduce dependence on freshwater and maintain a constant source of irrigation water throughout the year, waste waters of varying qualities can be used in agriculture. Generally, only waters that have had secondary treatment (i.e. physical and biological treatment) should be used to limit the risk of crop contamination and the health risk to workers.'''
There are two kinds of irrigation technologies that are appropriate for using treated wastewaters:
1)Drip irrigation where the water is dripped slowly on or near the root area; and
2)Surface water irrigation where water is routed overland in a series of dug channels or furrows.
To minimize evaporation and contact with pathogens, spray irrigation should be avoided.
Properly treated wastewater can significantly reduce dependence on freshwater, and/or improve crop yields by supplying increased water and nutrients to plants. Raw sewage or untreated blackwater should not be used, and even well-treated water should be used with caution. Long-term use of poorly or improperly treated water may cause long-term damage to the soil structure and its ability to hold water.
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{{procontable | pro=
- Reduces depletion of ground water and improves availability of drinking water. <br> - Reduced need for fertilizer. <br> - Low to moderate capital cost; low to moderate operating cost. <br> - Potential for local job creation and income generation. <br> - Low risk of pathogen transmission if water is properly pre-treated. <br> - Potential to improved health, self-reliance in community. | con=
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===Adequacy===
Generally, drip irrigation is the most appropriate irrigation method; it is especially good for arid and drought prone areas. Surface irrigation is prone to large losses from evaporation but requires little/ no infrastructure and may be appropriate in some situations.
There are potential health risks if water is not properly pre-treated (i.e. inadequate pathogen reduction). Soil quality can be degraded over time (e.g. accumulation of salts) if poorly treated waste water is applied. The application rate must be appropriate for the soil, crop and climate, or it could be damaging.
===Health Aspects/Acceptance===
Appropriate pre-treatment should precede any irrigation scheme to limit health risks to those who come in contact with the water. As well, depending on the degree of treatment that the effluent has undergone, it may be contaminated with the different chemicals that are discharged into the system. When effluent is used for irrigation, households and industries connected to the system should be made aware of the products that are and are not appropriate for discharging into the system.
Drip irrigation is the only type of irrigation that should be used with edible crops, and even then, care should be taken to prevent workers and harvested crops from coming in contact with the treated effluent. Despite safety concerns, irrigation with effluent is an effective way to recycle nutrients and water.
===Maintenance===
Drip irrigation systems must be cleaned periodically to remove any built-up solids. The pipes should be checked for leaks as they are prone to damage from rodents and humans. Drip irrigation is more costly than conventional irrigation, but has improved yields and decreased water/ operating costs.
===References===
* Ayers, RS. and Westcot, DW. (1994). [http://www.fao.org/docrep/003/T0234E/T0234E00.htm FAO Irrigation and Drainage Paper 29 Rev. 1. Water Quality for Agriculture]. FAO, Rome.
* WHO (2006). Guidelines for the safe use of wastewater, excreta and greywater- Volume 2: Wastewater and excreta use in agriculture. WHO, Geneva.
===Acknowledgements===
{{:Acknowledgements Sanitation}}