It has been estimated that today more than 2 billion people are affected by water shortage in over forty countries (WHO/UNICEF 2000) mostly related to rapid population growth and increasing water withdrawal for agricultural use. The irrigated agriculture accounts for approximately 70% of all freshwater withdrawals and more than 80% in the developing countries.
Many of the countries in the arid and semi-arid regions are already exploiting more than 40% of their renewable resources (AQUASTAT 2002). Due to these increasing demands, search for alternative water source is of paramount importance in water stress countries. In this context, wastewater reuse is becoming more valued, and certain countries are already using 100% of the treated wastewater for irrigation, domestic and industrial applications (as shown in graph).
The total land irrigated with raw or partially diluted wastewater is estimated at 20 millions hectares in fifty countries, which is approximately 10% of total irrigated land (World Water Development Report 2003).

Untreated wastewater contains a variety of pathogens, many of which are capable of survival in the environment, on crops or in the soil, and pose health risks to farmers and their families, consumers, and nearby communities. The joint FAO and WHO publication of Health Guidelines for the Safe Use of Wastewater, Excreta and Greywater are developed to address health protection and risk management as the basis to setting health-based targets in pathogen removal in context of technological feasibilities and socio-economic conditions.