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In 1993, the Ministry of Construction established the "National Urban Water Supply Quality Monitoring Network" (hereinafter referred to as the Monitoring Network). According to investigations, prior to the establishment of the Monitoring Network, only seven large water supply companies nationwide had the capability to test the 35 indicators stipulated in the then-current "Standards for Drinking Water Quality". In 1992, the Ministry of Construction proposed the "Urban Water Supply Industry Technological Progress Development Plan for 2000" (hereinafter referred to as the 2000 Plan), requiring Class I water companies to have the capability to test 89 water quality indicators. Currently, most monitoring stations have the capability to test 88 water quality indicators, and another six monitoring stations have the capability to perform mutagenicity testing (Ames test). The "Standards for Drinking Water Quality" published by the Ministry of Health in 2001 includes 96 testing items, and most monitoring stations do not yet have the capability to test some of the "non-routine items". However, some monitoring stations, based on local water quality needs, have the capability to test more than 100 items.
Water quality monitoring data is the most fundamental basis for water quality supervision. Therefore, strict requirements are placed on various aspects of testing institutions during laboratory certification/accreditation, including organizational structure, personnel qualifications, equipment, testing methods, working environment, and laboratory management. Testing institutions must pass the certification/accreditation review by the relevant departments of the State Administration for Quality and Technical Supervision before they are qualified to conduct urban water supply quality monitoring to ensure the accuracy and legality of the data. Currently, 36 monitoring stations in my country have obtained certification. A few monitoring stations have obtained accreditation.
Measurement of Physical Items
Of the 89 testing items stipulated in the "2000 Plan," 7 are physical measurements or sensory tests. Among them, the Ministry of Construction required that the turbidity measurement method in water be changed from the original diatomaceous earth visual turbidimetric method to the standard turbidimetric method (measured in NTU), with the turbidity standard being NTU, to align with international standards. This requirement improved the quality of water supply.
The measurement of the intensity of alpha and beta rays of radioactive substances involves concentrating the water sample and comparing it with a standard source using a counting system. If the intensity exceeds the standard, the health department should be consulted for radionuclide analysis and evaluation. Safety precautions must be taken during operation.
Detection of Inorganic Substances
The detection of inorganic anions: Previously, chlorides, sulfates, nitrates, nitrites, and fluorides in water were generally detected using titration or spectrophotometry. In recent years, to improve accuracy and simplify procedures, 50% of monitoring stations have switched to chromatography. However, this instrument is not suitable for detecting nitrites in drinking water; it can be used for detecting nitrites in raw water.
Using an ion chromatograph to inject multiple mixed standard solutions at once allows for the determination of the content of multiple substances, improving work efficiency.
—Detection of Inorganic Cations: Natural water contains many trace elements, some of which are beneficial to human health. Long-term consumption of water lacking certain trace elements or exceeding drinking water standards can lead to endemic diseases. Severe pollution can even increase the incidence of related diseases.
In the 1960s, the detection of these trace elements relied on cumbersome chemical analysis methods, which were costly, environmentally polluting, and lacked effective detection methods for some elements. With technological advancements, atomic absorption spectrophotometry was gradually adopted starting in the 1970s. Currently, all 36 monitoring stations use flameless atomic absorption spectrometry, which offers higher precision, accuracy, and detection limits than chemical methods, and is simpler and easier to perform. In recent years, hydride atomic fluorescence spectrometry has also been used to determine arsenic, mercury, and selenium in water, further improving detection accuracy. Both instruments can meet the requirements for specified detection items, making them essential instruments for monitoring stations. However, neither instrument can determine the specific elements present in an unknown water sample; they can only perform the detection of specified items and lack the ability to "scan" unknown water samples.
In the 1970s, we used a 2m grating spectrometer to determine elements in water. However, this instrument required large-scale water sample concentration, was cumbersome, and lacked sufficient accuracy. Its advantage was its ability to "search" for various elements in unknown water samples, making it suitable for the metallurgical, mining, and building materials industries.
In the 1980s, a major breakthrough occurred in analytical chemistry technology with the advent of inductively coupled plasma atomic emission spectrometry (ICP-AES), which is still considered the most ideal method for elemental detection. In 1980, two companies in the UK and Canada simultaneously launched commercial inductively coupled plasma mass spectrometry (ICP-MS). Its main principle is that the sample passes through a gas nebulizer, turning it into an aerosol. Then, using argon as a matrix, it enters a high-temperature radio frequency plasma. The ionizer is a sleeve with a high-frequency radiation ring outside the inner tube, generating high-frequency electric heating to a temperature as high as 100,000 K (≈9727℃). The aerosol is ionized inside the inner sleeve, while the outer sleeve is vented with gas or water to cool the outer wall of the inner sleeve. After ionization, the sample quickly passes through a sampler and enters the vacuum system of a mass spectrometer. The mass spectrometer generally uses a quadrupole mass spectrometer, which consists of four electrodes, each supplied with direct current and high-frequency current, generating two electric fields. When accelerated particles enter the two fields, they produce complex vibrations. By continuously changing the ratio of the high-frequency electric field to the direct current electric field (i.e., changing the high-frequency and direct current voltages), ions pass through the electric fields and enter electron multiplier tubes to generate signals (the intensity of which is proportional to the number of ions arriving). After being processed by a computer, qualitative analysis of the elements can be obtained. If a known standard sample is used for calibration, accurate quantitative analysis can be completed. The instrument's minimum detectable concentration for water samples is 0.08 μg/L, while our drinking water standard is generally 0.00 mg/L, thus fully meeting the requirements for drinking water testing. It is particularly useful for new water sources or water samples that have never been scanned by ICP-MS, helping to determine the presence of inorganic substances and prevent missed detections.
Simultaneously, this instrument can promptly detect the presence and concentration of inorganic toxic substances in sudden water pollution incidents and poisoning events. However, due to the high cost of ICP-MS and its large consumption of argon gas, the testing is expensive and difficult to widely adopt in the short term. According to incomplete statistics, monitoring stations in Shijiazhuang, Lanzhou, and Xining have ICP-AES spectrometers. Monitoring stations in Hohhot, Guangzhou, Shenzhen, Xi'an, Beijing, and the National Urban Water Supply Quality Center of the Ministry of Construction have already acquired ICP-MS spectrometers.
Detection of Organic Matter
Currently, the focus of global water pollution is the contamination of water by trace organic matter. More than 2,000 trace organic substances have been detected in water worldwide. In the United States, 767 organic chemical pollutants have been identified in water, of which 109 are carcinogenic and mutagenic. In 1990, the State Environmental Protection Administration, considering my country's national conditions, selected 14 categories and 68 substances as priority pollutants for water control. In recent years, developed countries, in addition to focusing on the hazards of carcinogenic, mutagenic, and teratogenic substances, have also paid special attention to the abnormal changes in aquatic organisms after pollution. This is due to the harmful effects of endocrine disruptors, such as cancer, infertility, birth defects, feminization, and reduced sperm count. Endocrine disruptors have been found to originate from pesticides, plastics, rubber plasticizers, and industrial pollutants. Relevant departments in my country are currently conducting investigations and research in this area.
Evaluating drinking water quality requires not only considering the toxicity of substances but, more importantly, understanding their content and comparing them to standards for evaluation. Therefore, accurate detection of organic matter content in water is crucial. Currently, gas chromatography (GC) and high-performance liquid chromatography (HPLC) are commonly used to detect trace organic substances in water.
Gas chromatography involves heating the sample before it enters the chromatographic column with a carrier gas, separating various complex compounds. These compounds then pass to separate detectors. There are four types of detectors: an electron capture detector (ECD) is often used for organochlorine compounds, while a flame photometric detector is often used for organosulfur and phosphorus pesticides. The electrical signal generated by the detector is compared with a standard sample of known concentration to determine the concentration of the substance. GC is suitable for determining organohalides produced after chlorination, pesticides, and organic compounds that are volatile upon heating.
High-performance liquid chromatography (HPLC) involves pumping the sample and solvent into a separation column packed with silica gel. This column separates various organic substances, which then pass to a detector (UV or fluorescence). The output signal is compared with a standard sample of known concentration to determine the sample's mass concentration. HPLC is generally used to analyze carcinogenic substances in water, such as phenols, polycyclic aromatic hydrocarbons (PAHs), and substances that decompose at high temperatures.
Generally, only about 20% of compounds in a gas chromatograph (GC) are introduced directly into the instrument without pretreatment, while 70% of compounds can be directly detected by a liquid chromatograph (LC). Both instruments are capable of detecting specific organic compounds in water and are essential basic instruments for monitoring stations; currently, all 36 monitoring stations are equipped with these two types of instruments.
When coupled with a mass spectrometer (MS), a GC-MS instrument can be used, similar to an ICP-MS instrument, with a "scanning" function. It can detect and quantify the types of organic compounds present in water samples. Coupled GC-MS analysis also has a detection function.
Furthermore, to reduce human error and improve work efficiency, automated flow injection (AFI) water quality analyzers are used to replace complex chemical analysis methods. These instruments are widely used for analyzing various substances in water, such as phenols, cyanides, and detergents. Currently, AFI automated flow injection analyzers have been installed in monitoring stations in Taiyuan, Hohhot, Wuhan, Ningbo, Guangzhou, Shenzhen, and Beijing.
Testing for Microorganisms in Water
The "Plan 2000" stipulated that, in order to align with international drinking water standards, testing for fecal coliform bacteria, fecal streptococci, and sulfite-reducing bacteria in source water and drinking water is required to assess the pollution status of water sources. Common testing methods include multi-tube fermentation for raw water and ultrafiltration membrane method for drinking water. Specific testing methods have been promulgated by the Ministry of Construction as industry standards (CJ/T148-2001).
Detection of Mutagenicity of Chemical Substances in Water
In the past 20 years, nearly 100 methods have been developed for testing the mutagenicity of chemical substances in water. However, only about 20 methods are frequently used to detect environmental pollution and alter mutagenicity. The "Plan 2000" stipulated the use of the Ames test. While the concordance rate between mutagenicity and carcinogenicity using this method still has some gaps, it remains the preferred method due to its rapid and readily available operation.
The principle is to determine whether the residue after concentrating a certain amount of water sample can cause gene mutations. Salmonella typhimurium is commonly used in this test, which assesses the ability of a Salmonella mutant to revert to the wild type using a test substance. The strain used is an auxotrophic type; it cannot synthesize histidine and cannot grow on histidine-deficient culture media. If the test substance induces a transformation from the mutant to the wild type, colonies will grow on the culture medium. The number of colonies indicates the strength of the mutagenicity of the test substance.
Currently, monitoring stations in Tianjin, Beijing, Shanghai, Shenzhen, Wuhan, and Kunming have this testing capability.
Testing for Waterborne Parasites
Giardia lamblia and Cryptosporidium are parasitic diseases prevalent worldwide and play a significant role in human infectious diseases. Drinking unclean water is a major route of transmission for these parasites. Currently, there is no specific treatment for Cryptosporidium infection, posing a serious threat to patients. Between 1965 and 1984, the United States reported over 90 outbreaks of Giardiasis. Japan also experienced an outbreak in 1996. In 1998, Sydney reported the detection of Giardia in tap water and urged residents to drink boiled water. my country's health authorities have also reported on this, especially in recent years with the spread of AIDS. The weakened immune systems of AIDS patients have made them susceptible to cryptosporidiosis, which has become a cause of death. This has drawn international attention, and relevant departments in my country are currently researching detection methods and related standards.
