Use of Hillside Ponds to Collect Unconventional Water for Irrigation Purposes

The increase of drought events represents an agricultural critical issue due to the reduced volumes of water for irrigation. To partially compensate this water crisis, it is necessary reusing water. In many countries, water reuse is hampered; the Water Reuse-Environment-European Commission asserts that only 1 billion m3/year of purified urban wastewater from member countries is destined for reuse against an estimated potential of 6 billion m3/year. This study aims to analyse the possibility of using hill ponds to accumulate unconventional water resources, such as purified wastewater from small settlements with a population of less than 2000 inhabitants. Hillside ponds are a specific category of tiny reservoirs of artificial origin, generally serving individual farms and used primarily for irrigation. Specifically, hillside ponds mainly store rainwater and runoff and sometimes convey spring water. Their construction is characterised by simplicity. They are mainly found in the Apennine environment. Their presence in various regions dedicated to cultivation has allowed the development of entire agro-industrial sectors. Furthermore, hillside ponds have stimulated a zootechnical system based on fodder production. According to community legislation, hill ponds can be integrated into the wastewater treatment or recovery plant with refinement tasks or can be part of the irrigation network. A survey was carried out on four hillside ponds located on the Sila Massif in Calabria (Italy), fed with rainwater and runoff, determining the concentrations of BOD5, COD, nutrients, metals, etc. in surface waters (20 cm) and on the bottom; concentrations of BOD5 between 5 and 7 mg/l, COD between 12 and 17 mg/l were found; it is noted that for class A tab. 2 EC Regulation 2020/741 provides for a BOD5 <10 mg/l to be used for irrigation purposes. These background values are extremely interesting as they enter into the sizing of these hill ponds to take into account the contribution of the bio-chemical processes. Hill ponds, therefore, can contribute to the increase of water resources in agriculture. However, it is necessary to point out that, without the due plant engineering measures, the tabular limits of the law could be exceeded due to background concentrations.