Bangkok’s clean water under threat: microplastics rise from plant to household taps

A study by Mahidol University and Thammasat University found that while Bangkok’s water treatment plant removes up to 81% of microplastics, contamination sharply increases in the city’s aging pipelines. The research warns that residents may ingest thousands of microplastic particles annually through tap water, underscoring the urgent need for infrastructure upgrades and advanced filtration.

A groundbreaking study by researchers from Mahidol University’s Faculty of Public Health and the School of Biochemical Engineering and Technology at Sirindhorn International Institute of Technology, Thammasat University, has unveiled alarming evidence of microplastic contamination in Bangkok’s drinking water. Published in Environmental Technology & Innovation, the research offers one of the first comprehensive examinations of how microplastics behave through both the treatment and distribution stages of a megacity’s water supply. Despite multiple purification steps, the study reveals that these microscopic pollutants persist, and even increase, as treated water travels through the city’s aging pipelines.

From River to Tap: Tracing the Path of Pollution

The research focused on a major water treatment plant (WTP) in Bangkok that processes 1.6 million cubic meters of water daily, drawing from the heavily polluted Chao Phraya River. Samples were collected at four treatment stages, coagulation, clarification, filtration, and chlorination, and from five household taps located 3 to 11 kilometers downstream. The results were striking: raw water contained 114 ± 46 microplastic particles per liter in the dry season and 56 ± 11 during the rainy season. The treatment plant removed between 75 and 81 percent of these particles, leaving 14–22 items per liter in the final treated water. Filtration proved most effective, while chlorination contributed little to further reduction. Seasonal differences were attributed to rainfall, with dilution reducing contamination during wet months and stagnation concentrating pollutants during dry periods.

The Rise of Secondary Contamination

Perhaps the most disturbing finding came from the household taps. Microplastic concentrations increased with distance from the WTP, indicating significant contamination within the distribution system. At just 3 km from the plant, particle counts rose to 31 ± 6 per liter, reaching 66 ± 27 per liter at 11 km, three times higher than at the source. The researchers linked this trend to pipeline degradation, biofilm detachment, and external infiltration through leaks and pressure fluctuations. Bangkok’s aging network, constructed from a mix of plastic and metal materials, likely releases and resuspends microplastics over time. Unlike newer systems in Rayong, Thailand, or Tianjin, China, where modern PVC and polyethylene pipes reduce contamination, the capital’s old infrastructure appears to act as a secondary generator of pollution.

What Lies Beneath: Composition and Size of the Pollutants

Microscopic analyses revealed that fragments were the most common microplastic form, followed by spheres and fibers. Fragments, accounting for more than half of all detected particles, originated largely from the breakdown of larger plastic debris in the environment. Chemically, polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET) dominated the samples, comprising up to 80 percent of total polymers. These materials are widely used in packaging and water pipe manufacturing and are notoriously buoyant and chemically resistant, qualities that allow them to bypass sedimentation and filtration processes. Smaller particles, especially those under 100 micrometers, were the most prevalent and the hardest to remove. They not only pass through treatment barriers but also pose higher biological risks due to their ability to penetrate human tissues.

The Health and Policy Imperative

The study’s implications for human health are deeply concerning. A typical Bangkok resident consuming two liters of tap water daily could ingest between 28 and 132 microplastic particles per day, amounting to 10,000–48,000 per year. These plastics may carry toxic additives like bisphenol A and heavy metals such as lead and cadmium, potentially triggering inflammatory or metabolic disorders. Although the World Health Organization (WHO) acknowledges that evidence on microplastic toxicity is still limited, it warns that such exposure cannot be ignored. The Bangkok study reinforces the urgency of improving both water treatment and distribution systems to minimize public exposure.

To combat this threat, the researchers propose a combination of technological upgrades and systemic reforms. Enhancing coagulation and flocculation efficiency, introducing oxidants like potassium permanganate, and adopting advanced membrane filtration systems such as ultrafiltration or reverse osmosis could push removal rates beyond 95 percent. Emerging solutions, including biochar adsorption, nanomaterial-enhanced filters, and magnetic extraction using nanoparticles, also show promise. Beyond technology, maintaining pipelines, monitoring real-time water quality, and promoting household-level filtration are vital to prevent recontamination.

A Call for Action

The study concludes that while Bangkok’s treatment plant performs reasonably well by regional standards, conventional methods are no longer sufficient. The city’s vast, aging distribution system has become an unexpected source of microplastics, undermining the effectiveness of the treatment process. The dominance of small, chemically stable polymers like PP and PE underscores their persistence and mobility in water networks. As the authors note, safeguarding urban drinking water in the age of plastic pollution will demand more than incremental improvements; it will require integrated water management, infrastructure renewal, and public health vigilance. For Bangkok and other rapidly urbanizing cities worldwide, this study is a stark reminder that the battle against plastic pollution must extend from riverbanks to kitchen taps.