## 1 Introduction
In addition to initial investments, it is also important to consider the significant resources required to manage and maintain water and sanitation infrastructure, as well as to ensure universal coverage. These recurring costs will exceed 1.4 to 1.6 times the infrastructure construction costs by 2029. However, it will be necessary to consider not only the investments required for the construction, operation and maintenance of infrastructure, but also funding for improving water quality, increasing the percentage of treated wastewater, increasing water efficiency, implementing integrated water resources management, protecting and restoring water ecosystems, and adopting climate-change-resilient technologies. Without a significant increase in investments in water projects, it will be nearly impossible to achieve the objectives set out in SDG 6. Therefore, a significant long-term financial commitment will be required, which will require particular attention on the sustainability of funding sources and the efficient management of resources [9]. There are three main means used worldwide to finance investments in the water services sector: tariffs, money transfers and taxes. Tariffs represent sums paid by users, a portion of which generally increases as the volumes of water consumed increase. In most cases, the rates provide for cost recovery, i.e., they are estimated to fully cover the costs of the services offered or specific parts of them. The remainder of the costs not recovered through tariffs is covered through a mix of money transfers and taxes. The funding sources used to fund the IWRM sector can vary significantly from one country to another. A recent study conducted by the World Bank has shown that only 35% of water companies can cover their operating and maintenance costs through the revenues generated by the tariffs, while only 14% can face all the economic costs associated with the supply of services. In addition,few companies can cover upfront capital costs, which often are equal to or exceed operating and maintenance costs. This occurs, for example, in the UK, where capital costs represent 49% of the total costs of a water company. As a consequence, the rest of the expenses are covered by subsidies, which can be explicit (direct money transfer) or implicit (such as subsidies in terms of the cost of production factors). In the absence of adequate subsidies, water managers are forced to postpone maintenance interventions, but this often causes a significant deterioration of the structures [10]. As regards the main European countries, in 2015, in per capita terms, 100 EUR per inhabitant per year was invested in the water sector in the United Kingdom, 80 EUR per inhabitant per year in Germany, 90 EUR per inhabitant per year in France and 30 EUR per inhabitant per year in Italy. In 2020, 175 EUR per inhabitant per year was invested in the water sector in the United Kingdom, 82 EUR per inhabitant per year in Germany, 149 EUR per inhabitant per year in France and 92 EUR per inhabitant per year in Italy (of which 56 EUR per inhabitant per year was allocated to investments in the IWRM) [11]. The water sector in Italy has not yet reached the performance of other European countries in terms of investments. To fill this gap, it would be necessary to invest 12.5 billion EUR by 2030. Furthermore, to guarantee the maintenance of water infrastructures, a further 6 billion EUR of annual investments would be needed (equivalent to around 100 EUR per inhabitant). However, water utilities are currently only investing around 3.5 billion EUR a year [12]. An attempt is being made to make up for this lack with the recent National Recovery and Resilience Plan (PNRR) prepared by the Italian government, which provides for the use of funds allocated by the European Union through the Next Generation EU program.