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On the evening of May 19, 2026, Weishi County in Henan Province, an ordinary northern county town, was disrupted by a day of heavy rain.

Residents in the county and urban areas suddenly began to experience symptoms of vomiting and diarrhea in batches, and hospitals and clinics formed long queues late at night. Students from some schools were collectively recruited, while adults and children from some families fell down together. On social media, the video footage of citizens queuing up and children holding their stomachs is heart wrenching.

Soon, a speculation spread in the community - there was a problem with the tap water.

This speculation is not groundless. At 4 pm that afternoon, Weishi County Jincai Water Affairs Co., Ltd. just issued a water outage notice: due to a sudden burst and leakage of the DN800 water supply main pipeline at the water plant, emergency repairs are needed and the entire city will be shut down. From 9pm that evening to 9am the next morning.

Stop drinking water and then experience collective diarrhea.

The timeline is there, no one can stop everyone from thinking in that direction.

Official investigation: Rainwater poured into the water source well

On the evening of May 20th, the joint investigation team of Weishi County issued the first notice with cautious wording - residents' symptoms have improved after outpatient treatment, and they have gradually returned home. Pathological samples have been sent for testing, and the cause is under investigation.

No direct tap water was provided.

But on May 21st, a press release from Xinhua News Agency provided the answer: rainwater flowed back into a tap water source well, causing sudden drinking water pollution.

After the heavy rain, the rainwater carried a large number of bacteria and pollutants on the surface and directly poured into this water source well. Through the water supply network, it flows into the faucets of thousands of households and into the stomachs of residents.

It's that simple. Just so direct.

We not only need to ask:

Firstly, where has the protection of the water source well gone.

According to the "Sanitary Standards for Drinking Water", centralized water supply sources need to be equipped with strict protective barriers to prevent rainwater and sewage from flowing back. Under normal circumstances, a water source well that has been properly protected will not be contaminated by a single rain. The wellhead is too low, the wellbore is damaged, and the isolation belt is missing - no matter which link is flawed, it all points to the same fact: routine inspections have gone through the motions.

Secondly, the disinfection of the water plant did not cover the bottom.

For the disinfection of tap water after sudden water source pollution, the tap water safety department did not do a good job in disinfection treatment. According to the regular flow disinfection process, it is necessary to carry out disinfection operations in emergency response stage and routine recovery stage according to the standardized process. The specific operation is as follows:

1. Emergency response phase (pollution investigation and control period)

Whole area evacuation and preliminary disinfection and sterilization: completely evacuate the polluted pipe network and reservoir, soak the tank wall and pipeline inner wall with high concentration disinfectant for disinfection and sterilization, and then flush and empty to remove residual pollutants.

Staged circulating disinfection of pipeline network: Before restoring water supply, excessive chlorine disinfection method is used: the residual free chlorine in the pipeline network water is increased to 0.5-1mg/L, and after circulating soaking for 2-4 hours, it is emptied and rinsed to completely kill the pathogens carried by pollutants.

Continuous water quality sampling: Samples are taken from the end of the pipeline every 2-4 hours to test for residual disinfectant and microbial indicators. Only after meeting the standards can the water supply be gradually restored.

2. Normal recovery stage (after meeting the standard water supply)

According to different disinfection methods, it is necessary to strictly control the remaining amount of disinfectant to ensure sustained antibacterial effect:

Chlorine dioxide disinfection: The residual chlorine dioxide in peripheral water should not be less than 0.02mg/L, which is suitable for controlling odor and color problems, and has fewer disinfection by-products. You can refer to using Xiuba brand chlorine dioxide disinfectant AB, and the specific dosage can be consulted with technical personnel according to the degree of pollution of the water source.

Liquid chlorine/sodium hypochlorite disinfection: Ensure that the residual free chlorine in the water at the end of the pipeline network is ≥ 0.05mg/L, which can continuously inhibit bacterial growth without producing excessive disinfection by-products.

Ozone+UV combined disinfection: Ozone disinfection requires a peripheral ozone level of ≥ 0.02mg/L. Combined with UV radiation, it can quickly kill stubborn pathogens such as Cryptosporidium, but a small amount of chlorine needs to be added later to maintain sustained antibacterial ability.

3. Additional disinfection requirements for secondary water supply

For the secondary water supply facilities in the community, additional completion is required:

Fully empty the water tank, manually clean the attachments on the inner wall, wipe and disinfect with chlorine containing disinfectant, let it stand for 30 minutes, and then rinse it clean.

According to the requirements of the new version of the standards, at least one comprehensive cleaning and disinfection+water quality testing should be completed each year, and the results should be publicly announced after disinfection.

Thirdly, why was there no warning for water quality monitoring.

They are doing tests every month. However, when encountering sudden rainwater backflow during the monthly inspection, the frequency of this "monthly inspection" exposes its fragility. There is a sufficient time window between the backflow of rainwater into polluted water sources and the large-scale occurrence of symptoms among residents. If water plants can monitor water quality more frequently and establish real-time warning mechanisms, even if problems are detected only a few hours in advance, they can avoid attracting a large number of residents.

The lesson of Weishi County can be applied to any county in the country. Today is heavy rain pouring into the water source well, tomorrow it may be construction that cuts off the pipeline, and the day after tomorrow it may be industrial wastewater seeping into the ground. For water supply companies, every extreme weather is a stress test; For regulatory authorities, every loophole needs to be discovered in advance during daily inspections.

For these ordinary people who turn on the faucet, what they want is actually very simple - water to drink. Don't worry, don't guess the water quality based on the weather, don't worry about whether the water is safe today.

Water is the source of life. If the most basic defense line of this city cannot be stabilized, all other developments will appear illusory.

Weishi County said that they have deeply learned from their lessons, will comprehensively strengthen water supply management, and will hold accountable according to law.

I just want to say one thing: Don't wait until the next heavy rain.