The reuse of wastewater is one of the main options being considered as a new source of water in regions where water is scarce. However wastewater reuse can also be linked with human health risks – for farmers as well as for crop consumers - as wastewater can contain enteric viruses, pathogenic bacteria and protozoa. Some chemical wastewater components, such as nitrogen, and phosphorus, may have both positive and negative effects on plant growth, crop yields, and the Environment. Others, such as suspended solids, high salt levels loads, can be disadvantageous for agricultural soils and irrigation infrastructure. In order to reduce negative impacts, many countries have adopted standards and guidelines, that regulate wastewater reuse in agriculture.

In the planning and implementation of water reclamation and reuse, the intended water reuse applications dictate the extent of wastewater treatment required, the quality of the reclaimed water, and the method of water distribution and application. Regulations issued for wastewater reuse in agriculture focus principally on sanitary and environmental protection, and usually refer to: wastewater treatment technology, reclaimed wastewater quality, irrigation practices, and control of areas or crop types where reclaimed water is used. The requirements are based primarily on defining the extent of needed treatment of wastewater together with numerical limits on bacteriological quality, turbidity and suspended solids.

However, the standards required for the safe use of wastewater and the amount and type of wastewater treatment needed are contentious. The cost of treating wastewater to conform to high microbiological standards can be so prohibitive that in many developing countries the use of untreated wastewater is effectively unregulated. Therefore, the health and environmental protection measures need to be tailored to suit the local balance between affordability and risk.

They should be:

• realistic in relation to local conditions (epidemiological, socio-cultural and environmental factors),

• affordable, and

• enforceable.

Where economic constraints limit the level of wastewater treatment that can be provided, a disease-control approach has been suggested, potentially using less strict microbiological guidelines and more management measures for health protection. A range of health protection measures including crop restriction, irrigation technique, human exposure control and chemotherapeutic intervention should all be considered in conjunction with partial wastewater treatment. In some cases, community interventions using health promotion programs and/or regular chemotherapy programs could be considered, in particular where no wastewater treatment is provided or where there is a time delay before treatment plants can be built.

Bahri 2002 has suggested that countries with substantial problems in treating wastewater in an adequate manner should undertake intermediate steps to mitigate the negative impacts:

• Introduce crop restrictions and standards for effluent reused for irrigation and other uses

• Apply source control of contaminants

• Apply appropriate irrigation, agricultural, harvest and public health practices that limit risks

• Improve extension and outreach activities to all stakeholders

• Upgrade the effluent quality from treatment plants

• On-farm use of storage and stabilization ponds

• The medium-term goal should be prohibition of all irrigation use of untreated wastewater.