The use of purified wastewater for irrigation: Possible strategies in the Capitanata area (Apulia, Italy)

The reuse of purified wastewater can supplement water availability for irrigation and limit withdrawals from groundwater which contribute to deteriorating its quality in many Italian coastal agricultural areas. The regulatory framework defined by EC Reg. 741/2020 specifies the legal and technical conditions, which from 2023 allow this use to be promoted in Italy. However, Italian agriculture is also differentiated in the ways in which farms obtain water for irrigation, and it is advisable to direct the treated wastewater towards the types that will then effectively reduce the use of groundwater. Our study seeks to identify these typologies by examining irrigation conditions in an important agricultural area of Southern Italy. Some districts of this territory are reached by collective irrigation networks of a Consortium that supply all the irrigation water; other areas are connected to those networks, but its supplies are lacking, and the farms also draw on underground aquifers; other areas are not reached by the collective network and groundwater is the only irrigation resource available. An econometric estimate of the irrigation demand in these areas defines whether the relationship between irrigation demand for groundwater and consortium is complementary or substitutive. This outlines the possible responses to the increase in consortium supplies with the introduction of treated wastewater, identifying the farm types to which those additional water resources can be allocated to reduce withdrawals from aquifers. A Seemingly Unrelated Regression Equations system of two irrigation water demand functions, from Consortium and from farm wells, is estimated with data from the National Information System for the Management of Water Resources in Agriculture (SIGRIAN) and the Farm Accountancy Data Network (FADN). The unitary costs of using each of these two sources are amongst the technical and economic regressors. The results indicate that in the farm type that uses both water sources, consortium and groundwater, there is a substitution relationship between these two sources. Also, the irrigation of these farms is the most responsive to current trends in the profitability of the various groups of crops, with the possibility of a further growth in the groundwater use. Supporting irrigation with treated wastewater on these farms would not induce rebound effects that increase the groundwater use: a greater irrigation supply of purified and conventional water at lower costs would instead reduce the use this water source.