A variety of factors, such as contamination of the water source, contamination of the pipeline network, and contamination of the secondary water supply, can lead to the emergence of disease-causing germs or toxic and harmful substances in drinking water.
When the color of tap water or barrel water from a drinking fountain is cloudy, there are suspended substances, there is a strange smell or the temperature of the water appears to be obviously abnormal, it is likely that water pollution has occurred.
Drinking water contamination
1, waterborne infectious diseases
Waterborne infectious disease pathogens
Bacteria: such as typhoid fever bacillus, paratyphoid fever bacillus, Vibrio cholerae, dysentery bacillus, pathogenic Escherichia coli, etc.
Viruses: such as hepatitis A and E viruses, polio virus, coxsackie virus, human rotavirus and adenovirus, etc.
Protozoa: e.g. Giardia lamblia, amoeba lysogenum, schistosomiasis, etc.
Between the occurrence of waterborne infectious diseases
Neglect of water hygiene protection: make the source of domestic drinking water, contaminated by fecal matter and domestic sewage containing pathogens. Inadequate purification and disinfection of water supply Drinking water is supplied to residents without the necessary purification and complete disinfection. Problems with the implementation of water transmission (storage and distribution), treated (purified and disinfected) drinking water in the process of water transmission and distribution and storage, due to leakage of the pipe network, the emergence of negative pressure, etc., re-contaminated by pathogens.
Characteristics of waterborne infectious diseases
Water source for a one-time serious contamination, showing an outbreak of epidemic state, can be a short period of time suddenly appeared a large number of cases, and the vast majority of cases of onset of the date of the disease, are concentrated in the same incubation period. If the water source is often, many times contaminated, showing the trend of epidemic, cases continue throughout the year.
The distribution of cases is consistent with the range of water supply from the contaminated source, and most cases have a history of drinking from the same source.
Once the source of contamination of drinking water is controlled and the drinking water is purified and disinfected, the epidemic of the disease will end quickly.
Spiral: mainly leptospirosis
They mainly come from human and animal feces, domestic sewage, hospital sewage, and wastewater from livestock slaughtering, leather and food industries.
Between the size of the scope of water transmission and the incidence of high and low, and the type of water source, the scope of the water supply (or the scope of water pollution), the degree and frequency of water contamination, the types of pathogens, the residents of the hygiene habits, drinking water purification and disinfection of measures, etc., all have a relationship.
2, chemical pollution caused by poisoning
3, surface water source pollution
drinking water source intake upstream, downstream and along the coast of the sanitary protection range, there are industrial wastewater, sewage, industrial residues, domestic garbage discharged. Drinking water intake within the scope of health protection, the river along the piling of industrial waste, domestic garbage; the construction of toxic and hazardous chemical warehouses, warehouses; the construction of loading and unloading of garbage, feces and toxic and hazardous chemicals of the dock. Pollution because of rainwater washing, leakage flowing into the river. Irrigation of farmland on both sides of the sanitary protection range of the drinking water source outlet with domestic sewage and industrial wastewater; use of pesticides that are difficult to degrade or highly toxic. Drinking water source water transmission (diversion) nullah along the coast, there are the above sources of pollution, especially close to the construction of fish ponds, grazing, etc..
4, groundwater pollution
Water wells and wells within the radius of influence, there are discharge of industrial wastewater, sewage seepage pits (wells), seepage toilets (dry latrines); each other's domestic garbage, industrial waste; farmland irrigation using industrial wastewater, sewage; the use of non-degradable or poisonous, toxic pesticides, chemical fertilizers. Within the radius of influence of the water source well, destroying the deep water soil layer, such as constructing drains and ditches for discharging industrial wastewater and domestic sewage without seepage control measures; constructing garbage and fecal matter treatment plants; landfilling of industrial wastes and domestic garbage; digging for sand and soil; and constructing fish ponds. Leakage from cracks in the well walls of water source wells, allowing biological or chemical pollutants to enter the water source wells through cracks and leaks. Recharge with domestic sewage, industrial wastewater, or surface runoff that flows through domestic waste dumps or industrial waste dumps.
5, drinking water pipeline network pollution
Pipe quality is poor cast iron pipe or ceramic pipe for drinking water pipe, cast iron pipe is easy to rust, ceramic pipe has permeability. Often due to corrosion, leakage triggered network pollution. Construction quality of the hidden dangers left behind (1) pipe connection before and after the connection is not flushed, so that the dirt accumulated in the pipeline, a long time, intermittent contamination of drinking water; construction of drinking water pipeline connection is not tight, resulting in leakage at the interface, once the water supply is stopped, the water pipe will form a negative pressure, the sewage outside of the water pipe, the pollutants will penetrate into the pipe, once the water supply is resumed, the pollutants inside the water pipe will be contaminated with drinking water. Pipes buried in the contaminated area. The so-called "polluted area" refers to garbage, toxic and hazardous chemical warehouses, warehouses; poultry and livestock farms; sewage culverts, sewage gutters, culverts and so on. Drinking water pipeline network through the above areas, if the corresponding health protection measures are not taken, drinking water is very susceptible to contamination.
Unreasonable design of drinking water: water pipes and non-potable water pipes are connected. If the drinking water pipe and fire water pipe connection, drinking water pipe and industrial water pipe connection, drinking water valve wells and sewage wells adjacent to the wall of the well without seepage control measures, etc.; drinking water pipe and sewage pipe distance, location is not appropriate. Laying the sewage pipe above the water pipe, when the water pipe is laid parallel to the sewage pipe, the distance between the horizontal is less than 1.5 meters, and the vertical distance is less than 0.5 meters, and when the water pipe is laid crosswise above the sewage pipe, the vertical distance is less than 0.4 meters and so on. In such cases, when the sewer pipe ruptures and the water main leaks, sewage can enter due to the negative pressure formed in the water main as a result of the water stoppage. Unauthorized connection by users Users without the consent of the water supply department, without adding health and safety measures, connect the drinking water pipe with other water pipes for dirt washing, soaking of articles, flushing of toilets, preparation of chemicals, etc. Once the water supply stops, negative pressure is generated in the drinking water pipe, and the sewage from other water pipes is sucked into the drinking water pipe.
Causes of pollution of secondary water supply facilities
Irrrational design: secondary water supply pipeline, and fire water pipeline, industrial water pipeline connection; storage tank (water tank) overflow pipe and drain pipe directly connected to the sewer pipeline; water tank of the water, no prevention of secondary pollution disinfection measures; water tank wall coating does not meet the hygiene requirements, the coating is prone to dissolution of the heck off.
The structure of the water tank is unreasonable: cement water tank inner wall is smooth, not conducive to cleaning; steel plate water tank is easy to rust, contamination of water quality; water tank observation holes (manholes, access holes) without cover, no lock; water tank without ventilation holes, overflow pipe openings without protective net cover.
Mismanagement: not regularly cleaned, disinfected; disinfection facilities can not function properly, no residual chlorine in the water; secondary water supply does not regularly test or monitor the project fails to meet the requirements; the environment around the water tank is dirty, the water tank cover is not tight and so on.
One of the incidents
The incident of excessive benzene in Lanzhou tap water in 2014 sounded an alarm for the water supply industry
The Lanzhou incident is a concentrated manifestation of the stage-by-stage contradictions in the development of China's water supply industry, which exposes the serious challenges faced by urban drinking water safety. Its high risk comes not only from environmental pollution and irrational urban layout that brings hidden dangers to water sources and water transmission, but also from the poor mechanism and chaotic management of China's water supply and other public utilities.
After the "4-11" tap water incident, Lanzhou drinking water safety issues finally accepted a face-to-face representatives of the National People's Congress "big test". the morning of December 26, 2014, the twenty-second meeting of the Standing Committee of the Municipal People's Congress of the twenty-fifth session of the meeting held Joint meeting, special inquiry on the city's drinking water safety.
Event two
Liaoyang residents drinking water pollution incident
Liaoyang City, Gongchangling District Water Supply Company on December 1, 2006, preliminary investigation, is due to the water wells themselves, such as broken filters, etc. 10 water supply trucks continue to deliver water to the residents, the basic solution to the 6026 households *** 17,000 people drinking water problems. Starting from November 25, 2006, Gongchangling District, Anping street tap water turbidity phenomenon, at first residents thought the water department in the repair pipeline, did not care. But a few days in a row, the tap water turbidity phenomenon is more serious, so residents reflect the situation to the community, the street. After the incident, Liaoyang City, immediately required the tap wells near all the relevant enterprises and projects that may cause water pollution to stop production and stop working. Streets were informed door-to-door, so that residents do not drink the existing tap water, set up water supply points in each community, arranged for 10 water trucks for the residents of the special water supply. Water company has been contaminated wells for cleaning; Environmental Protection Bureau of suspected sources of pollution, especially around the contaminated wells of solid, liquid emissions thoroughly removed; Urban Development Bureau commissioned the water company to connect the Tang River Phase II water supply pipeline, a temporary solution to the residents of drinking water. December 1, 2006, the Liaoyang City CDC test, the main indicators of the tap wells qualified, tap water has been basically in line with drinking water standards.
Event No. 3
In 1993, 400,000 people were infected with Cryptosporidium in the state of Wisconsin in the U.S., and there were more than 20 occurrences of Cryptosporidium mass infections worldwide. Cryptosporidium belongs to the water-borne pathogenic microorganisms, the most remarkable feature is that it has a thick wall capsule, which can exist for a long period of time in the water environment and can be resistant to chlorine. In our country, there has been no mass infection of Cryptosporidium.