Methodology to Set Regulations for Safe Reuse of Wastewater and Sludge for Agriculture in Developing Countries Based on a Scientific Approach and Following the New WHO Guidelines

Importance of Wastewater Reuse in Developing Countries

Wastewater is an important source of water and nutrients for irrigation in developing countries. Wastewater is used to irrigate land because of high water demand (70% of the total use worldwide), the availability of wastewater, its fertilizing properties due to nutrients and organic matter content, its low or zero cost, and the possibility of sowing all year round (Jimenez & Garduño, 2001; Jimenez, 2006). There is no complete global inventory on the extent of non-treated wastewater used to irrigate crops. Nevertheless, the global figure commonly cited is at least 20 million hectares in 50 countries (nearly 10% of total irrigated land). Certainly the use of this wastewater varies considerably from one country to another and occurs almost exclusively in the developing world, where 75% of the world’s irrigated land is located (UN, 2003). Figure 1 shows the 20 countries having the greatest number of hectares irrigated with untreated and treated wastewater, and it can be seen that the extent of untreated wastewater use is much greater than treated. It is of note that Figure 1 was constructed with relatively scarce amounts of information as data is often hidden due to the economic penalties a country might suffer when trading produce suspected to be irrigated with polluted water.

Figure 1.

The 20 countries reporting the largest surface irrigated with treated and untreated wastewater. Adapted from Jimenez & Asano (2008) and Kahn et al. (in press). Note: Information may vary from source to source. Some countries report agricultural wastewater use without mentioning the amount of hectares involved. (*Data are confusing.+No data are available, although the practice is reported.⁽¹⁾Surface might be greater.)

Agricultural use of wastewater has positive effects for farmers related mainly to improved income that directly helps health conditions by securing food and better nutrition in poor areas. Malnutrition plays a significant role in the death of 50 percent of all children in developing countries, amounting to 10.4 million deaths per year of children under the age of five (Rice et al., 2000). The negative effects of wastewater reuse are due to its pathogens and toxic chemical compounds content. The most important and rapid effects on human health are caused by pathogens when municipal wastewater is involved. More detail on positive and negative impacts on the use of wastewater for irrigation can be found in WHO (2006) and Jimenez (2006).