Water is regarded as the "source of life", and people can't live without water for a day. With the rise and expansion of cities, especially the rapid growth of population and the development of industry, water security problems have also emerged. Since the 1970s, water security has attracted extensive attention from the government, academia and civil society. 1972 After the first United Nations Conference on Environment and Development predicted the oil crisis, the next crisis was water. 1977, the United Nations once again stressed that water will become a profound social crisis. 1992 experts pointed out that in 2 1 century, water is the most important of the three resources: water, grain and energy. The shortage of water resources has become a major problem in the world today, and the pressure of water environment will also lead to social unrest, deterioration of public security and politicization of environmental issues (Li Fugui, 1997). With the environmental safety becoming a research hotspot, water environmental safety, as a relatively new research direction, is in the ascendant.

At present, people mostly study water security from the perspective of resource security, and water security refers to water resource security in a certain sense. Water resources security usually refers to the harm caused by the contradiction between supply and demand (quantity and quality) of water resources to social and economic development and human living environment. The carrying capacity of water resources is the basic measure to evaluate the security of water resources. Some scholars also believe that water resources security is an aspect of water security. For example, Xia Jun (2002) thinks that water security usually refers to the water hazard in the living environment of human society and the process of economic development, and water resources security is the most important aspect. Hongyang (1999) pointed out that water safety is the harm that water brings to human beings. Fang (2002) and Min Qingwen (2002) considered the safety of water resources and paid attention to the quantity and quality of water resources. Fang Ziyun (1998) discussed the security of water resources from the perspective of sustainable development. Some people say that the safety of water resources is the problem of more water and less dirty water.

However, water is not only a resource, but also an important part of the environment. Scholars Fang Ziyun, Wang Da (200 1a), Justin Ren and others (200 1) put forward that water environment is not only a water body related to water, but a complex related to water, aquatic organisms and pollution, a water body for storing, transporting and providing water resources, and also a space for aquatic organisms to survive and multiply and the ultimate destination of various pollutants. Liao Wengen (2002) also pointed out that water environment is a dynamic spatial system with water as the core. In the process of studying water resources carrying capacity, some people put forward the concept of water environmental carrying capacity, which is considered as the maximum capacity of a certain water area to accommodate sewage and pollutants under the condition that its water body can be continuously utilized and a good ecosystem can still be maintained (Wang Shucheng, 200 1). On the research of water environment security, many authors think that water environment security is a water pollution problem, such as (200 1) describing the water environment ecology in North China, Li (2002) analyzing the present situation of water environment in Liaoning Province, (2002) discussing the water environment problems in the sustainable development of small towns, and zhangyan (2002) talking about China's water environment. There are also studies on water quantity and water environmental safety. For example, Su Derong (2002) emphasized water quantity when analyzing the water security strategy of Gansu Province, and Wang Xiqin published a series of articles on ecological water demand research and river ecological water demand research, saying that ecological (environmental) water demand has gradually attracted the attention of experts and become an important aspect that can not be ignored. Of course, many scholars regard water quantity and water quality as the composition of water environmental security. At present, there is no accepted definition of water environmental safety, and the literature on water environmental safety is vague or just taken for granted. In my opinion, water environment security is different from the usual water resources security. Although the main content of water environmental security also refers to the problem of more water, less water and dirty water, it emphasizes that water is an environmental factor, and the water environment is a complete ecosystem, which is the unity of water quantity and water quality, including surface water environment and groundwater environment. From the perspective of environmental science, it is a dynamic concept, not from the perspective of resources, it is a concept of human utilization. To sum up, the author believes that the concept of water environmental security should be defined as: water maintains a certain amount of water and safe water quality conditions to maintain its normal ecosystem and ecological functions, to ensure the effective survival of aquatic organisms, and the surrounding environment is in a good state, so that the functions of the water environmental system can continue to play normally. At the same time, it can meet the needs of human production and life to a greater extent, so that the relationship between human beings and human groups is in a non-threatening state.

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