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Water is the source of Life. Since human beings got to know the importance of water， they have never ceased the development， utilization and dredging of water resources. At present， due to the uneven distribution of water resources， industrial development， agricultural plantation， water for living， fast growth of population， global warming and poor water management， human beings are facing an unprecedented crisis of water resource and water safety， and the problem is becoming increasingly serious. Therefore， promoting the civilization construction of water ecology is very urgent.
It is universally recognized that China is a country which suffers serious shortage of water. With the growth of population and the global climate change， these two factors will cause more serious shortage of water resources and pollution problems jointly. According to the data of China Water Resources Bulletin， in 2011 the total amount of water resources in China was 2.3 trillion cubic meters and the water resources per capita was only 1700 cubic meters per annum. Judged by the definition of UN， China belongs to the countries that lack water resources. At the same time， water resources of China are distributed unevenly and the current situation is： Abundant in south and west and inadequate in north and east; more in summer and less in winter; the regions with abundant water resources are often areas with small population and bad economy; and regions which lack water are often with large population and good economy， especially in North China where "most rivers are dry and most of water is polluted"， the contradiction of water resource security" and water demand is particularly prominent.
Since the total amount of the water resource is inadequate， the water resource per capita is seriously inadequate， and there are many problems of water pollution. From the end of the last century to the beginning of this century， the rapid development of city construction in China has once brought the problems of great rise in the demand of water and shortage of water resources. In order to solve these problems， the national government and many local governments have invested huge sums of money to adopt the method of taking the external water to make adjustments. However， long-distance water transfers have both advantages and disadvantages， especially in the area where the water is transferred from， the problem of damaging water ecology is becoming more and more serious. In addition， the compositional differences of the transferred water and the local water lead to dissolution and precipitation of the scale of pipes of tap water， and new pollution is coming into being， which is a big problem. Therefore， the mode of long distance water transfer is facing great difficulties to a certain extent. In fact， developed countries also have tough experiences. Thirty years ago， Austria carried out the transfer project of Murray River in south Australia， which led to problems including degeneration of the water ecological vegetation， damage of wetlands and salinization of land of the whole delta of south Australia， the losses caused by which exceeded the benefit brought by water transfer. Therefore， the Australian government has a profound reflection and decided not to transfer water by the means of "benefiting the present only and doing harm to the long-term benefits" and "benefiting the upstream while doing harm to the downstream"， but focus on ecological restoration. In recent years， many developed countries have set restrictions to long distance water transfer， especially inter-basin water transfers. Therefore， we should learn from it as early as possible. It can be seen from the experience of developed countries that after the process of urbanization comes to the middle stage， the requirement of water for life is unlikely to have great increase; judging from the rules of urban development of China， the water consumptions of cities tend to be stabilized and there is a declining trend and the crisis of lacking water has been gradually relieved. However， the nature of water transfer is "robbing Peter to pay Paul". Everybody knows transferring water to where it is needed， is just a math problem of addition and subtraction between different areas， but the recycling of water resources is a multiplication. It is believed that there are solutions that are more economical and ecological-friendly than long distance water transfer and that most of the cities in China have the ability to solve their problem of lacing water resources.
To achieve the goal， great importance should be attached to broadening sources， reducing the consumption， improving the utilization of water resources and ensuring the water safety of cities. The first： water saving of city must start from buildings， and the recycling of city sewage is a stable "second water source". China processes life sewage of cities which is up to 4 billion cubic meters every year， if it can be used to industries， administrations， landscape， ecological supplement and irrigation， a lot of water can be saved; Every 10 percent increase of the reusing rate of sewage equals to the 8 percent increase of water supply. The second： the collection and utilization of rainwater in cities is worth paying attention to. It is showed in the following three aspects： 1， to establish a wide rainwater collection system and set up rainwater collecting apparatus in city squares， buildings and basements， which can make the water resources increased by more than 30 percent. 2， to collect rainwater from city spaces such as buildings， city squares and parks， in this way， the amount of rainwater which goes directly into the sewer decreases and the pressure of city drainage system and water logging is reduced， and the purpose of saving water is achieved at the same time. 3， it can also solve the problem of rainwater pollution. For example， in Beijing， the annual rainfall is about 600 millimeters and if we can collect and make use of 20 percent of it， a built-up area with 1800 square kilometer can become water resources of 2.2 tons， which is equivalent to 14 percent of the total water supply of Beijing and able to meet one third to a half of the water demand of Beijing. We might as well take the economy and comprehensiveness of water-saving into account： to collect and utilize the rainwater of buildings， the investment of modular equipment is about 2000 RMB per ton and the operational cost less than 1 RMB per ton; the investment of urban wastewater recycling and reuse per ton is about 2500 RMB and the operational cost is only 1 to 2 RMB per ton. By water saving of cities， improving the reusing rate of industrial water and reducing pipeline leakage and other means， the potential of city water resource can be improved by more than 15 percent; the measures such as sewage treatment， on-spot water recycling， rainwater collection and utilization， seawater desalination and so on， can increase the amount of city water supply by more than 15 percent. Then it comes to agricultural water which accounts for 61 percent of the total water resources， if saving measures are taken （the effective utilization rate of agricultural irrigation is only 0.51， while that of the developed countries has reached 0.7 to 0.8）， there will be more potential， and if the 10 percent of agriculture water is saved， the current situation of shortage of city water resources will get better. The high-incidence period of pollution is the key period of restoring the ecology of water. According to the data released by China Environment Situation Bulletin， in recent years， the proportion of water in class I to class III has increased， and the proportion of water in class V has decreased， but according to the investigation results of the raw water of water plants in 35 large and medium-sized cities in 8 consecutive years released by the Ministry of Housing and Urban-Rural Development， the proportion of the number of standard samples of class II water has decreased from 24.8 percent in 2002 to 8.6 percent in 2009. It can be seen that the deteriorating trend of water environment of China has not been reversed fundamentally and the water shortage caused by pollution is the main factor threat to the water safety of cities. If the urbanization rate reaches 50%， the internationally recognized high-incidence period of water pollution crisis will come. In 2011， the urbanization rate of China reached 50 percent for the first time and water pollution incidents happened frequently. The high-incidence period of pollution is also the key period to treat pollution and retort the water ecological systems. Once the opportunity is missed， a very high price will be paid to treat the pollution. A multi-pronged measure of development philosophy， market mechanism， science and technology， laws and policies should be taken， and different means should be combined and applied flexibly to improve the efficiency of water utilization and solve the problems of safety of city water. The development philosophy must be， first， to combine advanced and suitable technologies， and safe water， sewage treatment and then recycling， energy recycling， rainwater collection and other measures should be used comprehensively. Second， the traditional water transfers and discharging should be transferred to ecological restoration. For example， transferring water to sweep away or thin the pollution should be changed to self purification of sewage， so as to accelerate the recovery of water ecological system. Third， to transfer from the demand-oriented unscientific mode to supply-oriented water saving mode. Fourth， to transfer from the extensive development of draining the pound to get all the fish， to the sustainable development with multiple use of water resources， and to complete water price reform through system and the market mechanism and give motivation to enterprises and citizens to save water. We believe firmly that as long as we adhere to scientific， efficient， low-cost and sustainable methods， we will be able to solve the problems of city water resources shortage and water safety.
It is universally recognized that China is a country which suffers serious shortage of water. With the growth of population and the global climate change， these two factors will cause more serious shortage of water resources and pollution problems jointly. According to the data of China Water Resources Bulletin， in 2011 the total amount of water resources in China was 2.3 trillion cubic meters and the water resources per capita was only 1700 cubic meters per annum. Judged by the definition of UN， China belongs to the countries that lack water resources. At the same time， water resources of China are distributed unevenly and the current situation is： Abundant in south and west and inadequate in north and east; more in summer and less in winter; the regions with abundant water resources are often areas with small population and bad economy; and regions which lack water are often with large population and good economy， especially in North China where "most rivers are dry and most of water is polluted"， the contradiction of water resource security" and water demand is particularly prominent.
Since the total amount of the water resource is inadequate， the water resource per capita is seriously inadequate， and there are many problems of water pollution. From the end of the last century to the beginning of this century， the rapid development of city construction in China has once brought the problems of great rise in the demand of water and shortage of water resources. In order to solve these problems， the national government and many local governments have invested huge sums of money to adopt the method of taking the external water to make adjustments. However， long-distance water transfers have both advantages and disadvantages， especially in the area where the water is transferred from， the problem of damaging water ecology is becoming more and more serious. In addition， the compositional differences of the transferred water and the local water lead to dissolution and precipitation of the scale of pipes of tap water， and new pollution is coming into being， which is a big problem. Therefore， the mode of long distance water transfer is facing great difficulties to a certain extent. In fact， developed countries also have tough experiences. Thirty years ago， Austria carried out the transfer project of Murray River in south Australia， which led to problems including degeneration of the water ecological vegetation， damage of wetlands and salinization of land of the whole delta of south Australia， the losses caused by which exceeded the benefit brought by water transfer. Therefore， the Australian government has a profound reflection and decided not to transfer water by the means of "benefiting the present only and doing harm to the long-term benefits" and "benefiting the upstream while doing harm to the downstream"， but focus on ecological restoration. In recent years， many developed countries have set restrictions to long distance water transfer， especially inter-basin water transfers. Therefore， we should learn from it as early as possible. It can be seen from the experience of developed countries that after the process of urbanization comes to the middle stage， the requirement of water for life is unlikely to have great increase; judging from the rules of urban development of China， the water consumptions of cities tend to be stabilized and there is a declining trend and the crisis of lacking water has been gradually relieved. However， the nature of water transfer is "robbing Peter to pay Paul". Everybody knows transferring water to where it is needed， is just a math problem of addition and subtraction between different areas， but the recycling of water resources is a multiplication. It is believed that there are solutions that are more economical and ecological-friendly than long distance water transfer and that most of the cities in China have the ability to solve their problem of lacing water resources.
To achieve the goal， great importance should be attached to broadening sources， reducing the consumption， improving the utilization of water resources and ensuring the water safety of cities. The first： water saving of city must start from buildings， and the recycling of city sewage is a stable "second water source". China processes life sewage of cities which is up to 4 billion cubic meters every year， if it can be used to industries， administrations， landscape， ecological supplement and irrigation， a lot of water can be saved; Every 10 percent increase of the reusing rate of sewage equals to the 8 percent increase of water supply. The second： the collection and utilization of rainwater in cities is worth paying attention to. It is showed in the following three aspects： 1， to establish a wide rainwater collection system and set up rainwater collecting apparatus in city squares， buildings and basements， which can make the water resources increased by more than 30 percent. 2， to collect rainwater from city spaces such as buildings， city squares and parks， in this way， the amount of rainwater which goes directly into the sewer decreases and the pressure of city drainage system and water logging is reduced， and the purpose of saving water is achieved at the same time. 3， it can also solve the problem of rainwater pollution. For example， in Beijing， the annual rainfall is about 600 millimeters and if we can collect and make use of 20 percent of it， a built-up area with 1800 square kilometer can become water resources of 2.2 tons， which is equivalent to 14 percent of the total water supply of Beijing and able to meet one third to a half of the water demand of Beijing. We might as well take the economy and comprehensiveness of water-saving into account： to collect and utilize the rainwater of buildings， the investment of modular equipment is about 2000 RMB per ton and the operational cost less than 1 RMB per ton; the investment of urban wastewater recycling and reuse per ton is about 2500 RMB and the operational cost is only 1 to 2 RMB per ton. By water saving of cities， improving the reusing rate of industrial water and reducing pipeline leakage and other means， the potential of city water resource can be improved by more than 15 percent; the measures such as sewage treatment， on-spot water recycling， rainwater collection and utilization， seawater desalination and so on， can increase the amount of city water supply by more than 15 percent. Then it comes to agricultural water which accounts for 61 percent of the total water resources， if saving measures are taken （the effective utilization rate of agricultural irrigation is only 0.51， while that of the developed countries has reached 0.7 to 0.8）， there will be more potential， and if the 10 percent of agriculture water is saved， the current situation of shortage of city water resources will get better. The high-incidence period of pollution is the key period of restoring the ecology of water. According to the data released by China Environment Situation Bulletin， in recent years， the proportion of water in class I to class III has increased， and the proportion of water in class V has decreased， but according to the investigation results of the raw water of water plants in 35 large and medium-sized cities in 8 consecutive years released by the Ministry of Housing and Urban-Rural Development， the proportion of the number of standard samples of class II water has decreased from 24.8 percent in 2002 to 8.6 percent in 2009. It can be seen that the deteriorating trend of water environment of China has not been reversed fundamentally and the water shortage caused by pollution is the main factor threat to the water safety of cities. If the urbanization rate reaches 50%， the internationally recognized high-incidence period of water pollution crisis will come. In 2011， the urbanization rate of China reached 50 percent for the first time and water pollution incidents happened frequently. The high-incidence period of pollution is also the key period to treat pollution and retort the water ecological systems. Once the opportunity is missed， a very high price will be paid to treat the pollution. A multi-pronged measure of development philosophy， market mechanism， science and technology， laws and policies should be taken， and different means should be combined and applied flexibly to improve the efficiency of water utilization and solve the problems of safety of city water. The development philosophy must be， first， to combine advanced and suitable technologies， and safe water， sewage treatment and then recycling， energy recycling， rainwater collection and other measures should be used comprehensively. Second， the traditional water transfers and discharging should be transferred to ecological restoration. For example， transferring water to sweep away or thin the pollution should be changed to self purification of sewage， so as to accelerate the recovery of water ecological system. Third， to transfer from the demand-oriented unscientific mode to supply-oriented water saving mode. Fourth， to transfer from the extensive development of draining the pound to get all the fish， to the sustainable development with multiple use of water resources， and to complete water price reform through system and the market mechanism and give motivation to enterprises and citizens to save water. We believe firmly that as long as we adhere to scientific， efficient， low-cost and sustainable methods， we will be able to solve the problems of city water resources shortage and water safety.