At present, in China, high-quality water supply generally refers to high-quality water supply in the community. Water supply methods mainly include barrel water supply and pipeline water supply. At present, some parts of Shanghai and some cities in China have established water purification supply stations, all of which are supplied by bottled water. "Pipeline water supply" refers to setting up water purification stations in residential areas to further treat, process and purify tap water, and adding independent high-quality drinking water supply pipelines on the basis of the original tap water pipeline system to deliver water to users for direct drinking by residents [1]. At the same time, urban water supply is regarded as general water.
There are two ways to supply bottled water: first, users go to the water purification station to collect it, empty the bottled water and charge it to the card; The second is to send water to the door, and charge a certain water fee according to the distance and floor height. The bottled water supply mode has been implemented in the family community of Tongji University (Tongji New Village) in Shanghai for some time. Practice has proved that it is feasible to build smaller residential areas within the scope of water supply. It is characterized by low investment and fast project implementation. Disadvantages are: ① users have no pipeline to supply water conveniently and flexibly; ② Due to various reasons (such as old age and infirmity, small family size, etc.). ), the utilization rate of drinking water will be affected to some extent; ③ If the bucket is not properly kept, it will bring about secondary pollution [2]. Pipeline water supply saves self-help or water supply, ensures water quality, is convenient to use, and is up to users to provide unlimited water supply. However, pipeline water supply needs another set of water supply system with strict hygiene requirements to enter the user's kitchen, which increases the project investment.
2. The concept of high-quality water supply abroad and its discussion.
In foreign countries, water supply by quality (double water distribution system) has a long history. The existing water supply systems in foreign countries all take drinking water system as the main water supply system in cities, and set up a pipe network system to supply low-quality water, reclaimed water or seawater for cleaning sanitary ware, washing vehicles, landscaping, watering roads and some industrial water (such as cooling water). This kind of system is called non-drinking water system, which is usually local or regional and is a supplement to the main water supply system. The establishment of non-drinking water system is obviously to make rational use of water resources and reduce the cost of water treatment. In this respect, the existing domestic water supply systems with different qualities, such as the industrial water system in Taopu Industrial Zone in Shanghai, the urban sewage reuse system in Qingdao, especially the seawater toilet flushing system in Hong Kong Special Administrative Region, and the existing or planned urban or regional water supply systems in other cities are no different from those in foreign countries in form and content.
As early as 1970s, Japan introduced a composite water supply system-the "middle waterway" system. The raw water of low-quality water in the system mainly comes from the sewage of buildings, residential areas and cities. After many treatments, it is reused in its original place. Because its water quality is inferior to that of "upper water" and superior to that of "lower water", it is called "reclaimed water". This not only ensures the urban water supply, but also protects the water environment, saves water resources and promotes the normal circulation of water system ecology, which is a good way to achieve multiple goals [3].
In 1983, AWWA Dual Distribution System Distribution Committee put forward "Guide to Quality Water Supply" to summarize the existing international experience of quality water supply, and hope to use this as a starting point to lay the foundation for establishing a unified standard and specification for quality water supply in the United States. Related terms are defined as [4] in the Quality Water Supply Guide:
Drinking water-water that meets federal and state water quality standards and is used for drinking, cooking and cleaning.
Non-potable water-Water used for non-potable purposes is only used for flushing sanitary wares (toilets) at home.
There is no precedent in the world that pipeline water supply is only for drinking, but there are two pipeline systems in China, namely drinking water.
(drinking water) and general water (sub-drinking water).
The U.S. Environmental Protection Agency believes that point-of-use devices and bottled water can only be used as temporary measures to improve water quality, because the use of water purifiers and bottled water is not considered as a way to meet the maximum pollutant concentration (MCLs) stipulated in the Safe Drinking Water Act Amendment (SDWAA), because they cannot provide all domestic water.
According to AWWA, the domestic water provided by AWWA to families, that is, the water from each faucet of users is drinkable.
What is worth discussing here is that another concept of high-quality water supply, which has become a hot spot in China at present, refers to providing a small amount of "pure water" for drinking (eating) through another pipe network, and using urban tap water as "general water". This is different from the existing or traditional water supply at home and abroad.
Oshima Research Office of Waseda University in Japan believes that modern cities have been able to implement water supply according to different purposes, high-tech water purification technology and water treatment facilities, and increasingly developed computer monitoring systems, which can provide safe and high-quality drinking water and all kinds of water with certain water quality standards for urban residents. Therefore, the original unified water supply mode in Japan should be changed and water supply should be carried out in different quality. Oshima Research Office also proposed "three kinds of water" supply systems in different regions [5]. This kind of water supply system is that urban water supply facilities supply water to residential areas according to the general standard of domestic water and even industrial water, and after being purified by water purification facilities in the community (high-quality drinking water), together with reclaimed water facilities in the community, it provides users with three kinds of water: the first kind of water is high-quality drinking water, which is mainly used for cooking in the kitchen; The second is general domestic water, including washing, sanitation, car washing, watering and so on. The third is low-quality water, which is specially used for flushing toilets. Generally speaking, the demand ratio of different water quality in residential areas is roughly as follows: drinking and cooking water (high-quality water) accounts for 15%, washing hands, bathing and washing clothes (standard tap water) accounts for 60%, and sanitation, watering flowers, car washing and other miscellaneous uses and flushing toilets (low-quality water) account for 25%. Due to the implementation of quality water supply in the community, the pipeline route is short and the monitoring and management are convenient. This "three kinds of water" water supply mode can not only meet people's demand for various water quality and quantity, but also make rational use of various water resources, reduce the discharge of pollutants, reduce the land scale of urban sewage treatment plants, and of course protect the water environment [3].
Through the above introduction, we find that this systematic way put forward by Oshima Research Laboratory in Japan integrates the current international (including domestic and foreign) discussions on high-quality water supply, which is a new development idea for high-quality water supply in the future.
3. Discussion on the implementation of quality water supply in China city.
3. 1 About high-quality water supply
At present, there is an understanding in China that only about 2% of drinking water in domestic water should meet the drinking water quality standards, and the other 98% of non-drinking water quality can not be strictly controlled at least at present. In fact, this is an incomplete understanding or a misunderstanding.
It is not necessary to treat all urban water consumption to the drinking water standard, but it is reasonable to consider the water consumption according to the drinking water standard far exceeding the total water consumption 1 ~ 2%. Considering the health needs and users' psychology, the proportion of potable water in domestic water at home and abroad should reach 40 ~ 50%, including kitchen washing and shower washing [6].
Martin Fox's preliminary research shows that harmful substances in water, especially volatile organic compounds, are absorbed by various parts of the human body in the following proportions: oral cavity (drinking and eating) 1/3, skin when washing and bathing 1/3, and respiratory tract with water vapor or aerosol when bathing 1/3[7]. In addition, a considerable part of clean water in life also needs qualified drinking water. Regarding the two ways of breathing and skin absorption, the following are explained separately.
Breathing: Because water contains many volatile substances, when it is heated, it will volatilize, diffuse in water vapor and aerosol, and enter the human respiratory tract and lungs through breathing, thus affecting human health. Studies have shown that when taking a bath with water containing TCE (trichloroethane), it is much more likely to inhale this chemical than to drink it directly. In fact, a person inhales 6-80 times more chemicals through his breath than through his mouth. For example, radon in water will volatilize after heating and enter the human body through breathing, which will form lung cancer after long-term accumulation. Therefore, the United States Environmental Protection Agency proposed that the maximum pollutant concentration target (MCLG) of radon in water should be zero at 1988.
There are many volatile organic compounds (VOCs) in water, so the EPA introduced a mathematical model to evaluate VOCs intake. Cathern et al. calculated with this model and concluded that if an adult weighing 70kg drinks 2 liters per day and the daily shower water consumption is 190l, the VOCs ingested in the shower are roughly equal to those ingested through drinking water. Andelaman reported the indoor respiratory intake caused by trichloroethylene in drinking water. Based on the drinking water consumption of 2L/ (person-day) and the shower water consumption of 40 ~ 95L/ (person-day), the respiratory intake of trichloroethylene in shower is several times that of drinking water [8]. Martin Fox and others also believe that skin absorption and respiratory intake are two important ways that cannot be ignored.
Skin absorption: Researchers from the University of Toronto and the Ontario Cancer Treatment and Research Foundation found that drinking chlorinated tap water or bathing with this tap water may lead to prostate cancer and bladder cancer. Comparing the residents who use tap water in cities and towns with those who use well water, it is found that the probability of bladder cancer in residents who use tap water for 35 years is 1.6 times higher than that in residents who use tap water for less than 0/0 years. In the same situation, the risk of bladder cancer is 1.5 times higher than the latter. Brown et al. studied the absorption of volatile organic compounds in water by skin. According to the adult's drinking water consumption of 2L/d, the infant's drinking water consumption is 1L/d, and the bathing time of them is15min/d; The ratio of skin absorption to oral intake of common volatile organic compounds in drinking water is 63/67 for adults and 40/60 for infants [8].
John Schaum of the U.S. Environmental Protection Agency and others believe that most pollutants do little harm to human skin when showering, except for a few substances with strong permeability. According to the relevant research data, the organic substances that can adsorb and penetrate into the skin and cause harm to health are: carbon tetrachloride, polycyclic aromatic hydrocarbons, benzene, dichlorobenzene, chlorobenzene, hexachlorobenzene, lower alkyl benzene, chloroform, polychlorinated biphenyls (PCB), grass green pesticides, nitroaniline, dinitrophenol, p-phenylenediamine, ethylenediamine, resorcinol, p-aminophenol, halogenated hydrocarbons and halogenated alcohols.
The World Health Organization (WHO) 1992 Edition "Guidelines for Drinking Water Quality" clearly points out that to determine the guidance value of chemicals in water, we should not only consider the drinking amount, but also consider the skin absorption and respiratory absorption when taking a shower.
From the above analysis, we know that there are many ways that domestic water directly affects human health, not just drinking one. Therefore, we believe that it is not enough to improve the quality of drinking water only, and we must improve the quality of our domestic water in an all-round way.
In addition, low-quality water or reclaimed water can be used for household miscellaneous water, such as road water for flushing toilets, vehicle cleaning, courtyard greening and watering courtyards. According to the current living standard of ordinary families in China, this water transfer accounts for about 20 ~ 40% of domestic water consumption. If water is supplied by quality, 60 ~ 80% of domestic water quality must meet the quality standard of drinking water, instead of 2% as now thought.
3.2 On Quality Water Supply
On the water quality of high quality water supply. There has been a lot of debate recently.
Supporters of drinking "pure water" believe that: ① water mainly plays a metabolic role in human body, and most factors or inorganic minerals in water cannot be directly absorbed by human body, and trace factors needed by human body can be supplemented by daily food such as grain and vegetables; ② Pure water has strong permeability, high solubility, easy absorption by human body, and more mellow and refreshing taste [1].
Dr. Martin Foucault of the United States pointed out in his book "Healthy Water" that "those who are in favor of drinking desalted water say that inorganic minerals (such as calcium, magnesium, selenium, etc.) are wrong after summarizing the main viewpoints and research results of healthy drinking water to prolong people's life. ) cannot be metabolized in water. " In fact, "minerals dissolved in water are easier and better absorbed than those in food". Dr. John Sorensen, an authority on mineral metabolism theory, believes that "minerals in drinking water can be well absorbed". The biggest harm of drinking pure water (reverse osmosis effluent) is that once this "hungry" water without minerals and trace factors enters human blood or other body fluids, according to the osmotic balance, it can not supplement trace factors and minerals in the human body, but seeps out reversely, enters the excretory fluid, and is finally excreted through excretion. In the long run, it will lead to the lack of minerals and trace elements in the human body, which will lead to many diseases [9].
According to relevant data, about 1/4 of the mineral elements needed by human body are supplied by drinking water. Pure water not only contains no mineral elements, but also is a good (pure) solvent. After drinking into the human body, it dissolves the existing mineral elements in the human body and excretes them. Sauev, an American doctor of medicine, analyzed 23 characteristics of water consumption in 92 cities and found that people who drink water with high TDS content are less likely to die of heart disease, cancer and chronic diseases than those who drink water with low TDS content [10].
Although there is no particularly strong data to prove which statement is more scientific and reasonable. However, from the comprehensive drinking water quality standards at home and abroad, it can be seen that although various water quality standards do not clearly point out that pure water cannot be used as daily drinking water, many secondary indicators clearly point out that pure water cannot be used as drinking water for a long time. For example, the EU requires that the hardness of drinking water must be greater than 60 mg CaCO3/L; For some trace elements, such as fluorine, iodine, selenium, etc., which are beneficial to human body to a certain extent, "limited indicators" and "limited indicators" have been set [1].
3.3 The negative impact of the implementation of quality water supply in China [1 1]
Compared with district or local water supply, "quality water supply" still refers to the way of providing drinking water with special pipes to solve the contradiction of tap water quality. The attractive premise of carrying out the idea of quality-based water supply in the whole city is to accept the assumption that drinking water only accounts for 1%~2% of the total urban water supply, and the main problem to be solved is the water quality of this 1% ~ 2%. As mentioned above, for domestic water consumption, the amount of water that needs to reach the quality of drinking water should not be less than 50% of domestic water consumption.
There are even high hopes for the attention of urban water supply in different quality, which implies a subconscious mind: it is unrealistic to control the decline of tap water quality and improve the quality of water supply by controlling water pollution and improving treatment technology, at least in the near 10 ~ 20 years. Solving the water quality problem of urban water supply is indeed a task that takes a long time to complete. However, if we are limited to the current difficulties and want to take a "shortcut", it may cause adverse consequences in economy and society.
One possible consequence of implementing urban water supply by quality is that efforts to protect water sources and improve water treatment technology have been relaxed in guiding ideology and specific operation. As a result, the water quality of the existing pipe network is gradually reduced to non-drinking water, and the drinking water supply is obviously less than the reasonable limit. As a result, all kinds of local advanced purification facilities and economic entities engaged in drinking water business flooded the market, and the actual water consumption of the whole city increased; However, the decentralized advanced treatment devices cannot be properly managed and reliably supervised. For example, household water purifiers can indeed alleviate the problem of substandard drinking water for some reasons, but improper use or poor operation and management will also have the opposite effect. According to the investigation by the State Bureau of Quality and Technical Supervision 1999, the qualified rate of bottled water in China is less than 50% [12].
The second consequence is long-term damage to the sustainable development of cities in the future. Urban water supply system is the main infrastructure of the city, which has a leading influence on the social and economic development of the city. It is the result of economic development and social progress to put forward higher requirements for drinking water quality. One-sided emphasis on the phased significance of "high-quality water supply" is to reduce the service standard and quality of urban water supply system, which is contrary to the requirements of sustainable economic and social development. According to the financial resources, it is reasonable and even necessary to solve the water quality problem of urban water supply by stages according to the severity, but we should not easily adopt the method of overall water supply by quality. The construction and investment recovery period of urban comprehensive water supply system is very long. If it is easy to implement, it will "set things right" in a few years, and this repetition may cause obvious harm to the local economy and environment.
At present, the concept of quality-based water supply in China, on the one hand, evades the responsibility of improving the water quality of tap water industry, the main body of water supply, on the other hand, it is easy to lead people to misunderstand the health of drinking water.
3.4 Our Views and Conclusions
The basic task of urban water supply system is to provide tap water with standard water quality, sufficient water quantity and moderate water price for life and production. At present, urban water supply by quality has become a hot concept in China, and it can't be said that it is a relatively perfect water supply mode only to ensure the drinking and eating water quality of 2L ~ 3L/ (person-day).
Improving the water quality of urban water supply is a long-term task. In the process of striving to achieve this task, it is a transitional measure to provide "pure water" by implementing quality-based local water supply through direct drinking water pipes or water purification rooms, which is an extension and supplement to the existing urban water supply system before the water quality of urban tap water has reached people's higher water quality requirements. In newly-built residential quarters, especially in the case of high-quality groundwater resources, it is an attractive temporary measure to try to supply water in different grades. As a temporary measure to meet the drinking water demand of people with high consumption level, supplying pure water through pipelines in newly-built middle and high-grade commercial residential quarters with limited groundwater exploitation can also play an active role on the basis of accumulating experience and improving management. This method has been tried out in the living quarters of some cities, which has certain positive significance and is conducive to accumulating experience for the water supply industry in China and other developing countries, but it is unreasonable to implement it in the whole city and has obvious adverse consequences.
In particular, it should be pointed out that this method of supplying water with a small amount of pipes dedicated to drinking water is not the advanced experience of developed countries. In developed countries, this is unacceptable; In newly industrialized countries, there is no similar application report. Therefore, tap water should not be reduced to the general level (semi-drinking or even non-drinking) because of the existence of this water supply mode, and tap water should not be regarded as low-quality water. For this, we must have correct and scientific propaganda and guidance, and don't step into misunderstanding.
4. Conclusion
Urban tap water supply system is the main water supply system for any type of water supply with different water quality. Management (including pipe network and secondary water supply) should be strengthened to improve the water quality, so that its drinking water quality standard can be in line with international standards as soon as possible. This is the long-term and fundamental solution. At present, there are 35 testing indexes stipulated in the Water Quality Standard for Drinking Water, and the revised standards of the Ministry of Health and the Ministry of Construction will be raised to 64 and 88 respectively (88 in the United States and 133 in WHO), and the water quality hygiene standard is higher, which will better meet people's needs. In order to achieve the development goal of urban water supply in China, it is necessary not only to strengthen water source protection, improve the treatment process of water plants, improve the technical status of water transmission and distribution systems, and solve the problem of secondary pollution, but also to reform the operating mechanism of urban water supply industry, gradually realize the marketization of water prices, and fundamentally play the leading role of urban water supply industry.
refer to
1. Dong Li Liu Yun, present situation of pipeline water supply in China, water supply and drainage in China, 1999, 15 (1), 24-25.
2. Li Yi, Fan, Feasibility Study of High-quality Drinking Water Project in Jinhua Community, Pudong New Area, Shanghai, Water Purification Technology,1997,59 (1), 25-27.
3. Wang, Quality Water Supply and Reclaimed Water System, World Architecture, 1998, 1, 28-3 1.
4. Wang, Meng Xiurong, On Urban Water Supply by Quality, Urban Water Supply, 2000,3, 19-2 1.
5. Introduction to Urban Environment and Equipment, edited by Wang, Zhejiang University Press,1June 1998, 88-94.
6. Guan Weiping, Ji, On Urban Water Supply with Different Quality, Heilongjiang Environmental Bulletin, 2000,24 (2), 63-64.
7. Martin Fox, Healthy Water, translated by Zhou Rong, 1996.
8. Li Tian, Liu Suiqing, Discussion on the Limitation and Function of Different Quality Water Supply in Solving the Water Quality Problem of Urban Drinking Water, Water Supply and Drainage,1999,25 (2), 4-8)
9. Wang Lin, Safe and Quality Drinking Water, Urban Environment and Urban Ecology, 2000, 13 (1), 1-3.
10. He Jingsheng, Pure Water, Ultrapure Water and Drinking Water, Sichuan Geology, 1999, 19(3), 233-240.
1 1. Guan Weiping, Ji,. On urban water supply by quality. Heilongjiang Environmental Bulletin, 2000,24 (2), 63-64)
12. Zhang, Du, Study on Small High-quality Drinking Water Complete Equipment, Heilongjiang Environmental Bulletin, 2000,24 (2), 74-76)