Introduction: Water is one of the key components for sustaining human life. It plays a very important role in the achievement of food security, personal hygiene and health, development of economic sectors (industry, services, and agriculture), and also in protection of natural ecosystems and environmental services. Considering the close relationship between sustainability of water resources and production of foodstuff and energy, weather, economic growth, and human security, the most important threat the world faces today is water insecurity. Hence, protection of water resources is a serious matter and integrated water resources management (IWRM) is the only action plan for achieving this goal. The IWRM is an approach in which the process of economic and social development of countries is coordinated and consistent with water and land sources so that sustainability of vital ecosystems and their future renewability and also satisfaction of water needs are not endangered. That is why the present research studied and compared the status on the IWRM in selected countries across the world using the Water Poverty Index (WPI).    
Materials and Methods: The WPI, which was widely accepted with the realization of the multidimensional nature of water scarcity, shows the relationship between the level of human well-being and the various dimensions of water resources. As a comprehensive tool that combines the physical, social, economic, and environmental dimensions associated with water, the WPI allows
a better understanding of the complexities of water resources management. It has five components including resources, access, capacity, use, and environment. Each component is measured by using some indices. The value of each one is standardized so that its numerical value is in the range of zero to 100 for the purpose of aggregation and interpretation. After calculating the values of the WPI, the countries across the world can be grouped into five different categories based on the Central Limit Theorem (CLT). Savings can be made in government time and costs by determining the most important components and variables influencing the WPI. Therefore, the sensitivity of the WPI was also analyzed to better understand the extent to which each component or variable impacted the fluctuations in the WPI. To conduct the present research, the required data for the period 2000-2020 were obtained from the statistical resources of the World Bank and Food and Agriculture Organization of the United Nations (FAO) and their mean values were used in the measuring process. The software packages of Excel 2019 and Arc GIS were used to perform the calculations and spatial analysis of the WPI, respectively.
Results and Discussion: The results of descriptive statistics related to the WPI and its components showed that its minimum and maximum values for the countries across the world were 34.12 for Niger and 74.81 for Guyana – which indicated a range of variation of 40.09. In addition, the estimated mean value of the global WPI was 58.60. Study of the descriptive statistics related to the five components of the WPI for the countries worldwide also revealed that the resources component had the lowest mean value (-27.88), the lowest minimum value (-19.29) and the largest range of variation (109.78). Based on these statistics, we can say that the global situation with respect to the resource component was inappropriate and water distribution was not balanced. The capacity component had the second lowest mean value (43.47), which suggested that the economic and social capacity in water resources management across the world was not suitable. Furthermore, this component had the smallest range of variation (52.31), which suggested that the countries worldwide indicated the least difference in the capacity component. As for the access component also, the results showed that it had the largest mean value (80.02), which indicated that the countries across the world seemed to be in better conditions in terms of access to wastewater disposal and treatment systems. In addition, this component had the largest standard deviation (24.8), which meant that access to water treatment and wastewater disposal and treatment systems was not balanced worldwide. The use component had a high standard deviation (22.07) among the five components, whereas the lowest standard deviation (9.49) was obtained for the environment component. The results of classifying the countries with respect to the WPI and spatial analysis also indicated that 25 countries faced water insecurity and 12 confronted low water security. In addition, 31 countries had suitable water security and 16 enjoyed 100 percent water security. In general, most countries faced the water insecurity and the low water security were located in Africa and Asia. Iran, with a WPI value of 58.55, ranked 82 among the nations in the world with respect to the water security. The results related to the sensitivity analysis of the WPI also illustrated that based on the Variable Contribution (VC) index, the access component with the value of 2.27 percent contributed the most to the positive fluctuations in the WPI and the capacity component with the value of -2.27 percent the least. Furthermore, omission of the access component or the resources component changed the standard deviation of the WPI by 5.58 and 16 units on average, respectively. Based on the results of contribution of variable in the fluctuations of the average water poverty index known as ME, the WPI values decreased by 5.58 percent and 16 units on average if the resources component or the access component was omitted, respectively.
Conclusion and Suggestions: The journey of the countries across the world towards sustainable development can be facilitated if they know the current situation in regard to sustainability of water resources and strike a balance between water resources and water use. The study results showed that 25 countries lacked sustainability of water resources and 12 others confronted low sustainability of water resources; in addition, 31 countries enjoyed suitable sustainability of water resources and 16 had 100 percent sustainability of water resources. According to the results, there is 100 percent sustainability of water resources in most European and American countries, whereas the majority of Asian and African countries have the lowest level of sustainability of water resources as shown by their WPI values. Since the access, capacity, resources, use, and environment components are highly important in higher levels of sustainability or high levels of unsustainability of water resources, it is suggested that a comprehensive approach be used for continuously assessing sustainability of water resources in various regions in order to develop integrated water resources management.