Recently, residents in parts of Hangzhou’s Yuhang District reported a noticeable odd smell in their tap water, sparking widespread concern. As the source of life, the taste and odor of tap water directly impact our daily lives and sense of security. So, where do these strange tastes come from? What are the hidden “culprits” behind them? And how does the water supply industry tackle these challenges? Today, we’ll break it down for you from a professional perspective, incorporating the latest research findings.

01 Incident Recap: The Tap Water Odor Controversy in Yuhang

On the morning of July 16, abnormal odors were detected in tap water in parts of Renhe and Liangzhu Subdistricts in Yuhang District, Hangzhou. On July 19, the Yuhang District People’s Government released an official statement:

At 8:00 a.m. on July 16, the Renhe Water Plant detected abnormal odor indicators in the water supply. After sampling and analysis, the plant immediately activated its emergency response plan for water supply incidents, switched water sources, and effectively controlled the water quality, ensuring the safety of the treated water. An investigation was promptly launched, and a task force comprising national and provincial experts was formed. Preliminary findings indicate that the odor was caused by sulfur ether compounds produced by the anaerobic degradation of algae under specific natural climate conditions. The exact cause is still under investigation, and results will be disclosed in due course. With many rumors circulating online, including claims of “sewage contamination,” local authorities have taken legal action against the spread of misinformation. The public is urged not to believe or propagate such rumors.

02 Professional Insight: What’s Behind the Strange Taste in Tap Water?

The issue of unusual odors in tap water (technically referred to as “off-flavors”) is neither rare nor unsolvable. Chinese researchers have conducted systematic studies on the topic (see Water & Wastewater Engineering, Issue 11, 2024: Major Odorants in Drinking Water and Their Control Strategies). Key findings include:

Extreme Sensitivity to Odors: Humans can detect certain odor-causing compounds at concentrations as low as 10 ng/L.
Limited Removal by Conventional Processes: Traditional water treatment methods—coagulation, sedimentation, filtration, and disinfection (e.g., chlorination)—are often ineffective at eliminating many odor-causing substances.
Primary Culprits:
- Earthy/Musty Smells: One of the most common types, primarily caused by compounds like 2-methylisoborneol (2-MIB) and geosmin, which are metabolites of cyanobacteria (e.g., Planktothrix, Oscillatoria).
- Rotten/Swampy/Fishy Smells: Another common type, often resulting from sulfur compounds like dimethyl disulfide and dimethyl trisulfide, produced by the anaerobic decomposition of organic matter (e.g., algae).
- Chemical/Solvent/Plastic Smells: Less common, usually caused by leaks or discharges of synthetic chemicals.

03 How to Combat These Odor-Causing Compounds? A Dual Defense at the Source and Plant

To address odor issues, the water supply industry employs multi-layered strategies from source to treatment plant:

2. Enhanced Treatment at Water Plants (Critical Barrier)

Activated Carbon Adsorption (Primary Tool): Powdered activated carbon (PAC) is the most widely used and effective method for addressing seasonal or sudden odor incidents.
Ozone-Biological Activated Carbon (O3-BAC) Advanced Treatment (Long-Term Solution): This is the optimal choice for tackling persistent or complex odor issues while improving overall water quality.
Advanced Oxidation Processes (AOPs): Techniques like O3/H2O2 (ozone-hydrogen peroxide) and UV/H2O2 (ultraviolet-hydrogen peroxide) are highly effective at removing stubborn algal odors like 2-MIB and geosmin.
Optimizing Conventional Processes and Operations:
- Use pre-oxidants cautiously
- Enhance sludge removal
- Avoid simultaneous dosing of PAC and oxidants

Conclusion

A glass of clear, odorless, and safe tap water is the result of complex source protection, technological innovation, and meticulous management. The odor incident in Yuhang is both a challenge and an opportunity to drive continuous improvement in water quality control. Researchers’ ongoing exploration of odor-causing compounds and the water industry’s relentless pursuit of better treatment methods are all aimed at safeguarding the “sense of security” on everyone’s lips. We will continue to monitor the latest developments in drinking water safety and provide more expert insights.

References:
1. Chunmiao, Su Ming, Wang Qi, et al. Major Odorants in Drinking Water and Their Control Strategies [J]. Water & Wastewater Engineering, 2024, 50(11): 32-39.
2. Reports from The Paper, People’s Daily, and other sources.

Expert Reviewer: Wang Xiaoxiao, Associate Researcher and PhD Supervisor, School of Environment, Tsinghua University

This article was edited and compiled by the Water & Wastewater Engineering magazine’s new media team. Please credit the source when reposting.

Note: This article is reprinted from the Water & Wastewater Engineering WeChat public account.

--- title: "What’s Behind the Strange Taste in Tap Water?" date: 2025-07-21 lang: en authors: - "Min Yang et al." categories: - blog description: "Unusual odor in Yuhang tap water: The incident of abnormal 'sewage-like' smell in Hangzhou's Yuhang District" --- Recently, residents in parts of Hangzhou’s Yuhang District reported a noticeable odd smell in their tap water, sparking widespread concern. As the source of life, the taste and odor of tap water directly impact our daily lives and sense of security. So, where do these strange tastes come from? What are the hidden "culprits" behind them? And how does the water supply industry tackle these challenges? Today, we’ll break it down for you from a professional perspective, incorporating the latest research findings. # 01 Incident Recap: The Tap Water Odor Controversy in Yuhang On the morning of July 16, abnormal odors were detected in tap water in parts of Renhe and Liangzhu Subdistricts in Yuhang District, Hangzhou. On July 19, the Yuhang District People’s Government released an official statement: > At 8:00 a.m. on July 16, the Renhe Water Plant detected abnormal odor indicators in the water supply. After sampling and analysis, the plant immediately activated its emergency response plan for water supply incidents, switched water sources, and effectively controlled the water quality, ensuring the safety of the treated water. An investigation was promptly launched, and a task force comprising national and provincial experts was formed. Preliminary findings indicate that the odor was caused by sulfur ether compounds produced by the anaerobic degradation of algae under specific natural climate conditions. The exact cause is still under investigation, and results will be disclosed in due course. With many rumors circulating online, including claims of "sewage contamination," local authorities have taken legal action against the spread of misinformation. The public is urged not to believe or propagate such rumors. # 02 Professional Insight: What’s Behind the Strange Taste in Tap Water? The issue of unusual odors in tap water (technically referred to as "off-flavors") is neither rare nor unsolvable. Chinese researchers have conducted systematic studies on the topic (see *Water & Wastewater Engineering*, Issue 11, 2024: *Major Odorants in Drinking Water and Their Control Strategies*). Key findings include: 1. **Extreme Sensitivity to Odors**: Humans can detect certain odor-causing compounds at concentrations as low as 10 ng/L. 2. **Limited Removal by Conventional Processes**: Traditional water treatment methods—coagulation, sedimentation, filtration, and disinfection (e.g., chlorination)—are often ineffective at eliminating many odor-causing substances. 3. **Primary Culprits**: - **Earthy/Musty Smells**: One of the most common types, primarily caused by compounds like 2-methylisoborneol (2-MIB) and geosmin, which are metabolites of cyanobacteria (e.g., *Planktothrix*, *Oscillatoria*). - **Rotten/Swampy/Fishy Smells**: Another common type, often resulting from sulfur compounds like dimethyl disulfide and dimethyl trisulfide, produced by the anaerobic decomposition of organic matter (e.g., algae). - **Chemical/Solvent/Plastic Smells**: Less common, usually caused by leaks or discharges of synthetic chemicals. # 03 How to Combat These Odor-Causing Compounds? A Dual Defense at the Source and Plant To address odor issues, the water supply industry employs multi-layered strategies from source to treatment plant: ## 1. Source Control (Long-Term Solution, Especially for Algae-Related Odors) - **"Light Adjustment for Algae Suppression"**: By scientifically adjusting reservoir water levels or turbidity (light attenuation), underwater light intensity can be modified to restrict the growth of odor-producing algae. - **Optimizing Hydraulic Conditions**: For smaller reservoirs, reducing hydraulic retention time and accelerating water exchange can effectively curb algae growth. - **Caution with Algaecides**: While chemicals like copper sulfate can quickly kill algae, they pose ecological risks and should be used sparingly. ## 2. Enhanced Treatment at Water Plants (Critical Barrier) - **Activated Carbon Adsorption (Primary Tool)**: Powdered activated carbon (PAC) is the most widely used and effective method for addressing seasonal or sudden odor incidents. - **Ozone-Biological Activated Carbon (O3-BAC) Advanced Treatment (Long-Term Solution)**: This is the optimal choice for tackling persistent or complex odor issues while improving overall water quality. - **Advanced Oxidation Processes (AOPs)**: Techniques like O3/H2O2 (ozone-hydrogen peroxide) and UV/H2O2 (ultraviolet-hydrogen peroxide) are highly effective at removing stubborn algal odors like 2-MIB and geosmin. - **Optimizing Conventional Processes and Operations**: - Use pre-oxidants cautiously - Enhance sludge removal - Avoid simultaneous dosing of PAC and oxidants # Conclusion A glass of clear, odorless, and safe tap water is the result of complex source protection, technological innovation, and meticulous management. The odor incident in Yuhang is both a challenge and an opportunity to drive continuous improvement in water quality control. Researchers’ ongoing exploration of odor-causing compounds and the water industry’s relentless pursuit of better treatment methods are all aimed at safeguarding the "sense of security" on everyone’s lips. We will continue to monitor the latest developments in drinking water safety and provide more expert insights. **References**: 1. Chunmiao, Su Ming, Wang Qi, et al. Major Odorants in Drinking Water and Their Control Strategies [J]. *Water & Wastewater Engineering*, 2024, 50(11): 32-39. 2. Reports from *The Paper*, *People’s Daily*, and other sources. **Expert Reviewer**: Wang Xiaoxiao, Associate Researcher and PhD Supervisor, School of Environment, Tsinghua University > This article was edited and compiled by the *Water & Wastewater Engineering* magazine’s new media team. Please credit the source when reposting. Note: This article is reprinted from the [*Water & Wastewater Engineering* WeChat public account](https://mp.weixin.qq.com/s?__biz=MzA3MjM1MTEwNg==&mid=2655085338&idx=1&sn=23c11a2c026fec5b7d84bab2a6890a29&scene=21&poc_token=HHMlf2ijKl5CVKCSWQKG-4fH2qMciuKWvJ7J49_c).