By Wang Yanbing

When it is raining cats and dogs and there are ponds everywhere, you will definitely pray that the sun will shine again immediately after the rain. But you maybe don't know that, for a city in shortage of water, such rain is a kind of "Heaven-sent gift". People start focusing on rain water, the available natural resource, and taking many practical actions while the current fresh water resources on the earth become less and less. As it is an effective manner to solve water shortage in a city and improve urban ecological environment, the use of rain water in a city becomes more and more important and affects everybody's life.

Alleviate the water shortage in the city through rain water utilization

Taking Shanghai, the city where we live in, as an example, although there are rivers, lakes, creeks and surrounding sea, it still is a city in need of water. According to the statistics of Shanghai Water Bureau, the "good water" that we can use accounts for only a few portion of the above said water resources. At present the maximum daily output of tap water in Shanghai is 10 million tons but the daily water consumption reaches 9 million tons already and nearly touches the limit level.

We can learn a lot from the ways of using rain water in some overseas cities for the purpose of collecting and recycling rain water to solve water shortage. For example, the underground tunnel water storage system is built in Chicago, U.S.A. to prevent flood and use rain water; British London Thames River Company developed a Century Dome Demonstration Project where water of 500 m3, of which 100m3 is collected from rain water, is recycled everyday and used for flushing toilet in this building.

Compared to cities in developed countries, the use of urban water resources in the past was mainly focused on exploitation of surface and underground water resources while ignoring recycling and collection runoff rain water in the city. As a result, such valuable rain water resource was wasted. Along with the urban expansion, the loss of rain water becomes more and more severe. Therefore, on one hand, the shortage of water is serious, the underground water is over-exploited and the underground water level is decreasing year by year; on the other hand, the huge discharge of rain water brings a series of environmental problems such as water logging and deteriorating urban ecological environment. If the abundant rain water resource can be used properly in Shanghai, not only the resource can be utilized and the pressure on flood prevention will be decreased significantly, but also the pressure on urban sewage system in the case of storms will be alleviated and the water logging will be minimized.

Use of rain water joining in "Green EXPO"

Nine ministries and commissions including the Ministry of Science and Technology of the People's Republic of China, Shanghai Expo Coordination Bureau, and the Commission of Science and Technology of Shanghai have jointly launched special technological taskforces for EXPO. One research theme is "key technology for collection and recycling of rain water in EXPO Park" and an expert team has conducted careful research and in depth study.

The persons in charge of the said topic, Mr. Zhang Chen, Zhou Weiguo with Shanghai Municipal Engineering Design and Research Institute, describe the ideal use of rain water resource in the city and introduce a lot of overseas advanced technologies and examples. They believe that the use of rain water in China is still in research stage, and the comprehensive treatment, collection and ecotype use of rain water in the city, will be of great benefit to integrate the use of resources, flood prevention, urban landscaping and environment improvement. Such integration of research, study and practical use of rain water in the EXPO Park completely complies with the concept of "Green EXPO and Ecological EXPO".

The World EXPO Shanghai China 2010 will be a global event focusing on "City" theme. Various problems occurring in the urban development progress around the world will become topics of this EXPO. As the urbanization speeds up in the world, the sound development of city's ecological environment is facing severe challenges and the pressures on the urban ecological environment and natural resources increases. Among these challenges the water shortage is a major issue to be faced by the current community. It shows unusual significance to conduct research on this topic under such background.

Smart use of rain water in the city

With the urban development taken into account, the expert team for this subject has summarized two available ways for using rain water, collection and recycling of roof rain water, and storage and penetration of rain water.

Roof rain water is easy for collection and recycling so it has the highest useable value. According to the current studies, the water quality of first runoff roof rain water is comparatively poor due to decomposition of roof materials and air pollutants. The abandonment of rain water should be considered in the initial stage of recycling roof runoff in order to reduce burden of treatment, investment and operation cost. Experts believe that the design of roof and selection of material are effective means for controlling water quality of roof rain water runoff. The rain water from roof can be used directly for flushing toilet, watering landscapes or creating water scenery through a little treatment or without treatment after abandonment of rain water in the initial stage.

The storage and penetration of rain water can reduce the increased storm runoff due to urbanization, delay the concentration time, loosen the load on sewage system and play an important role in disaster prevention and reduction. At the same time, it also can retain underground water and prevent ground settling. The rain water is purified by penetration through active soil layer and clearances between crushed stones so that pollution can be reduced.

This team has also put forward their proposals on how to apply these study results in the EXPO.

There are a lot of newly built and remained large buildings in Shanghai EXPO Park. Some roofs can be built into green roofs if possible and the roof rain water can be recycled for municipal purposes through simple treatment following abandonment of rain water in the initial stage. Considering unevenness of rainfall, the water from Huangpu River, after proper treatment, can be used as supplementary water for rain water recycling system in summer for the purpose of watering landscapes and roads in the EXPO Park. This can reduce consumption of tap water, save water resource and reduce costs.

There are large area of green lands and plenty of sidewalks and squares in the Expo Park greenery system. In construction of the park, some rain water can be retained and preserved through low-lied landscaping and penetrable surface layer. On one hand, the burden on the sewage system and investment of water collection pipeline project can be reduced and the pressure on flood prevention system can be released because of improvement and strengthening of penetration, on the other hand a part of pollution can be eliminated and the pollution load in the city can be reduced thanks to storage and penetration of rain water.

There is no doubt that water, the source of life, will be in full supply through reasonable use of rain water in the near future. It will not only solve the water shortage in the city but also provide better conditions for creation of ecological environment in the city.