The study by IWMI deals with a case study of urban wastewater as a valuable resource for agriculture in Haroonabad, Pakistan. Farming communities in water-scarce regions increasingly practice the use of urban wastewater in agriculture. Untreated urban wastewater is generally considered unacceptable for direct use because of potential health risks. However, in many parts of the world, poor farmers in peri-urban areas use untreated wastewater. This practice is likely to continue in the foreseeable future due to the high investment cost associated with the installation of treatment facilities.
In order to systematically document the advantages and disadvantages of using untreated urban wastewater, the case study was undertaken in Haroonabad, which is a small town in the southern Punjab in Pakistan. Information on costs and benefits associated with wastewater use was obtained by monitoring a group of 20 wastewater farmers and a group of 20 non-wastewater farmers over a one-year period. Water and nutrient applications and the quality of groundwater and soil were investigated in nine fields, of which some were irrigated with wastewater and others with regular canal water. To assess the human health impacts, a comparison was done between a settlement where wastewater irrigation was practiced and one where regular canal water was used.
The greatest benefit for farmers using wastewater was the reliable water supply, which allowed them to grow high-value vegetable crops. However, water and nutrient applications to wastewater-irrigated fields were excessive in relation to the recommended values. From this we can deduce that, with the improved distribution of wastewater, more farmers could benefit from the water and the nutrients it contains.
Although there were signs of accumulation of heavy metals in wastewater-irrigated soils, the values did not exceed internationally recommended standards. However, there were negative health impacts, especially in the form of an increased prevalence of hookworm infections among wastewater farmers.
Irrigation with untreated wastewater is practiced in most cities in Pakistan because of its high productivity. Wastewater use also has an indirect benefit associated with the reduction of pollutants discharged into natural watercourses. The study concludes that there is a need to identify methods to prevent or lower the health risks associated with the use of untreated urban wastewater while maintaining or increasing its socioeconomic and environmental benefits under the prevailing social and economic conditions.
