Why Does Tap Water Have An Odor? — Decoding Water Quality Safety And Protecting Drinking Water Health

Recently, the phenomenon of tap water having an odor has concerned countless people. Official investigation results show that the odor originates from sulfur-containing compounds produced by the anaerobic degradation of algae in high-temperature environments. So, where exactly does the odor in tap water come from? How can we scientifically prevent this? Today, let’s delve deeper to uncover the truth behind the odor in tap water and explore effective solutions.

I. The Source of the Odor: A “Dual Challenge” from Nature and the Water Supply Network

The odor in tap water is not a coincidence; its causes primarily stem from two major factors, creating a “dual challenge”:

Water source pollution: In high-temperature weather, eutrophic water bodies are prone to algal blooms. During their growth, metabolism, and decomposition, these algae produce sulfur-containing compounds such as dimethyl sulfide and dimethyl trisulfide. These compounds have an extremely low odor threshold, meaning that even at concentrations as low as one part per billion, people can detect distinct foul odors such as rotten or fishy smells.

Pipeline and secondary water supply issues:

Iron pipelines are prone to corrosion after prolonged use. During pipeline repairs or water source switches, changes in water flow may dislodge rust layers from the pipeline walls, causing “yellow water” in tap water and a metallic taste.

If secondary water supply tanks are not cleaned and disinfected promptly, they may harbor bacteria, algae, and other microorganisms, leading to odors and water quality issues.

II. Excessive levels of sulfide compounds: Indirect impact on water turbidity and color

Sulfide compounds (such as dimethyl sulfide and dimethyl trisulfide) are soluble organic compounds. While their excessive levels do not directly determine water turbidity and color, they can indirectly influence these parameters through a series of mechanisms:

1. Impact on turbidity

Role of algae-derived particles: The production of sulfur-containing compounds often accompanies the proliferation of algae. During their metabolic processes and upon death, algae release organic debris and microbial metabolic byproducts in the form of suspended particles. These particles, once introduced into the water supply system, may leave residual microscopic particles even after conventional treatment, leading to increased water turbidity.

Chain reaction of pipeline corrosion: Some sulfur-containing compounds (such as hydrogen sulfide) have corrosive properties, and their prolonged presence can accelerate the corrosion of iron pipelines. During pipeline repairs, water source switches, or pipeline flushing, changes in water flow can dislodge rust layers, causing large amounts of iron oxide (Fe₂O₃) and colloidal substances to be released, directly leading to a sharp increase in turbidity at the water outlet and the appearance of “yellow water.”

2. Impact on color

Reaction with metal ions: During chlorine disinfection of tap water, sulfur-containing compounds may react with iron, manganese, and other metal ions in the water to form colored precipitates such as FeS and Fe(OH)₃, causing the water to appear yellowish-brown or blackish-brown. For example, the “tea-colored” tap water reported by some residents may be related to the combined effects of sulfur oxide products and metal ions.

Cumulative effects of algal metabolites: Sulfide compounds often coexist with organic matter such as humic substances produced by algal metabolism. These organic substances have light-absorbing properties, significantly increasing water color and causing it to appear yellow-green or brownish-red, affecting visual perception.

III. Solutions: Balancing Technology and Standards to Strengthen Water Quality Safety Measures

Due to the high volatility and strong solubility of sulfur-containing compounds, conventional water treatment processes (such as precipitation and filtration) struggle to remove them quickly and thoroughly. To prevent the recurrence of “odorous water” incidents, the key lies in establishing a three-pronged protective system combining “excess prevention + process monitoring + emergency detection”:

1. Strictly adhere to national standards (GB 5749-2022)

The “Sanitary Standards for Drinking Water” (GB 5749-2022) sets 97 stringent indicators for drinking water quality, comprehensively safeguarding drinking water safety. Among these, indicators closely related to sulfur-containing ether compound exceedances include:

Microbiological indicators: such as total coliform bacteria and total bacterial count, ensuring water bodies are free from pathogenic contamination.

Toxicological indicators: including heavy metals (lead, arsenic, etc.), pesticide residues, volatile organic compounds, etc., to prevent potential risks to human health.

Sensory and general chemical indicators: including turbidity, color, odor, pH value, visible particles, etc., directly affecting the sensory experience and basic safety of drinking water.

Disinfectant indicators: such as free chlorine, chlorine dioxide, ozone, etc., to ensure disinfection effectiveness and inhibit microbial growth.

Radioactive indicators: total alpha radioactivity and total beta radioactivity, etc., to ensure the water is free from radioactive risks.

Water supply companies must regularly test water quality to strictly ensure that the water leaving the plant is colorless, odorless, and free of microbial contamination.

2. Establish an online monitoring network for the entire water supply process

Install online water quality monitoring instruments at key treatment stages in water treatment plants, such as coagulation and sedimentation tanks, filter tanks, and clear water tanks, to monitor treatment effectiveness in real time and ensure that all indicators for water leaving the plant meet standards.

Monitoring points should be established at critical nodes such as main pipelines in the water distribution network, secondary water supply tanks, and residential area endpoints. Key indicators to monitor include free chlorine (to ensure continuous disinfection effectiveness), turbidity (to prevent pipeline sediment contamination), and color (to avoid sensory abnormalities). In the event of abnormalities (such as turbidity or color exceeding standards), the system will automatically trigger an alarm, aiding in rapid tracing and isolating the pollution source. When both turbidity and color increase simultaneously, heightened vigilance is required for sulfur-containing compounds and their derivative pollutants. Combining methods such as purging and trapping gas chromatography-mass spectrometry for odor detection can confirm whether pollutants exceed standards.

3. Enhancing emergency rapid testing capabilities

In the event of sudden water quality incidents, portable water quality analyzers should be deployed for “on-site rapid testing” to identify the type of pollutant within 5 minutes, providing timely guidance for emergency response measures (such as adding activated carbon adsorption or switching to backup water sources) to minimize the impact.

The recurrence of tap water odor incidents serves as a stark reminder: water quality safety is the bottom line for public welfare. By strictly enforcing national standards, leveraging technological means to enhance monitoring, and mobilizing public attention, we can build a more robust water quality defense system. Choose PROBEST water quality analyzers to ensure your drinking water safety with professional technology!