CHIANG RAI – For many people in Chiang Rai, tap water used to be a point of pride. The city was known for its clean water drawn from the Kok River basin. Today, that proud image has faded and been replaced with anxiety and mistrust.
Confirmed reports of arsenic and heavy metals in the Kok River and its tributaries now come from state agencies, independent laboratories, and local communities. More and more households have stopped drinking, and some have even stopped using tap water altogether.
The Provincial Waterworks Authority (PWA) Chiang Rai branch insists that treated water still meets the Department of Health standard. Test results show arsenic in tap water at below 0.001 milligrams per litre, well under the legal limit of 0.01 milligrams per litre. For many residents, those numbers are not enough to restore trust.
The crisis is no longer just about pollution. It has become a crisis of confidence that cuts to a basic right: access to clean and safe water for more than 120,000 people in Chiang Rai City and downstream communities.
In this context, the plan by PWA Chiang Rai to move its raw water intake from the Kok River to the Lao River, with a total budget of 2,176 million baht, has drawn close attention. For many people, it looks like the only realistic step that can be taken now, while cross‑border mining pollution from Shan State in Myanmar remains too complex for local authorities to fix alone.
Contaminated Kok River, worried riverside communities: “Is our water still safe to use?”
On 25 November 2025, at the rice barn in Ban Tha Bon Dai, Moo 1, Wiang Chai District, Chiang Rai, the Right Bank Water Users Group 1 of Chiang Rai Dam held its 2025/2026 annual meeting.
At the top of the agenda was one key concern: contamination of the Kok River and its tributaries with arsenic and other heavy metals. The meeting was attended by Chiang Rai governor Chucheep Pongchai, executives from Chiang Rai Provincial Administrative Organisation (PAO) led by deputy PAO chief Sutherapong Wanchaitanawong, and other agencies.
The water users group, led by its chair, Prathompong Rittiphaeng, reported that tests had found arsenic and heavy metals at several points along the Kok River and some branches, in some places above legal limits. They raised serious doubts that the pollution comes from gold and rare earth mines located in the upper reaches of the Kok in Shan State, Myanmar.
For more than 750 farming households that rely on this water, the problem feels very close to home. It affects food security, income, and peace of mind. Many farmers worry that toxins may build up in rice and other crops. Falling rice prices add pressure, so they now shoulder both economic hardship and the hidden costs of pollution.
Deputy PAO chief Sutherapong told Nakorn News that Chiang Rai PAO will not sit still. He said the PAO will act as a key coordinator, bringing together data from all agencies, including water quality, river ecology, and social impacts. The goal is to push for a structured clean‑up and stronger control of pollution in the Kok River basin.
He stressed that this is not just an environmental issue. It is a matter of health rights and community rights for everyone who lives along the Kok.
The Kok River crisis is part of a much wider pattern
In November 2025, the Stimson Center, a US‑based think tank focusing on security and the environment, released a report on mining in mainland Southeast Asia. Using satellite images, the study identified more than 2,400 mines that may be discharging toxic substances into major river basins.
The researchers mapped at least 366 alluvial mines, 359 heap leach mines, and 77 in‑situ leaching (ISL) rare earth mines. These types of operations often use dangerous chemicals such as cyanide, mercury, and ammonium sulphate. When released into rivers, these substances can build up in sediment and the food chain. Over time, they create big, long‑term risks for the health of communities along the Mekong, Salween, Kok, and other rivers.
Human rights groups in Shan State, such as the Shan Human Rights Foundation, along with academic studies and reports by Kachin research centres, point to Chinese ownership and investment in many of the rare earth and gold mines in the Kok headwaters. Chinese operators manage and control the technical side. Local communities provide labour and are the first to be exposed to toxic substances.
This context matches the observations of Associate Professor Dr Suebsakul Kijjanukol from the School of Social Innovation at Mae Fah Luang University, who is part of a Kok River monitoring network. He notes that many of the rare earth and gold mines in Shan State use old, dirty technologies that China has already phased out at home, only to see them exported to neighbouring countries with weaker environmental safeguards.
He links this to the memorandum of understanding on critical minerals between Thailand and the United States, which aims to increase the supply of rare earth elements for the global industry. Some researchers warn that the push for energy security and green technologies may drive an expansion of mining in the region. If there are no strict controls, that expansion could further threaten the rights of downstream communities.
PWA Chiang Rai: “Our system still works, but we need to move because people do not accept the Kok.”
On the water supply side, PWA Chiang Rai branch manager Apisak Sawaddirak explains how the plan to move the raw water source from the Kok River to the Lao River first came about.
The starting point was the detection of arsenic in the Kok River last year. Test results showed values below the Department of Health limit, yet public concern grew rapidly.
In the past, the Chiang Rai plant used a standard treatment process that relied mainly on alum and lime. Once heavy metals were found, the team upgraded the system. They added a pre‑chlorination step by injecting chlorine before coagulation to help separate heavy metals.
They also began using polyaluminium chloride (PACl) and sodium hydroxide (NaOH) to speed up sedimentation, so that more arsenic‑laden particles fall to the bottom before the water moves on to intermediate chlorination and filtration.
The raw water in the Kok has always been challenging. During floods, turbidity can reach 10,000 NTU, while the normal average is around 180 NTU. The plant now controls turbidity before filtration to under 4 NTU, and keeps filtered water below 1 NTU. These limits are stricter than the basic legal standard.
Apisak stresses that all chemicals used are approved for drinking water treatment and are handled under strict laboratory control, with regular verification by the Department of Health.
At the same time, he speaks plainly about the core issue.
“The key reason is that people no longer accept the Kok as their water source. Even if we can treat the water to meet the standard, it does not matter if people still feel uneasy. PWA must respond to that feeling. We are not moving because the plant cannot cope. We are moving because we want people to have full confidence.”
From his professional view, the current system can handle the Kok’s water quality. But he accepts that restoring the river to a truly clean state would need long‑term cross‑border cooperation. That process will take many years, and it is not fair to ask residents to wait while living with ongoing risks.
Switching to the Lao River: 2,176 million baht for a 100‑year investment in safe water
The relocation plan sets out a new raw water intake and treatment plant at Mae Lao Weir on the Lao River. From there, treated water will be pumped through a high‑pressure main to Chiang Rai city over a distance of about 34 kilometres.
The total planned investment is 2,176 million baht. PWA expects to submit the proposal for funding in the 2028 fiscal year. If approved, construction could start in 2028 or 2029.
This project is not only about escaping pollution in the Kok. It is also designed to expand the water supply network along the new pipeline from Mae Lao into the city. Communities that previously sat outside the service area will then be able to connect to a reliable, safer supply.
PWA forecasts that the number of customer households will rise from 41,539 in 2025 to 66,639 in 2046.
For the short term, PWA Chiang Rai has requested a 5 million baht budget to upgrade the chemical dosing system at the Wang Kham plant. The goal is to control dosing more accurately and increase safety while residents wait for the long‑term solution.
Associate Professor Dr Suebsakul sees the multi‑billion baht price tag as high but reasonable when weighed against the long‑term health of the province.
“In simple terms, spending a few billion baht now can buy safety for the whole province for the next 100 years. That is a better choice than waiting for a wave of health problems later on.”
When Chiang Rai residents stop drinking and using tap water, trust figures do not match what people feel
Any attempt to understand this crisis feels empty without listening to those who actually use the water.
Mathuros Plengsai, who lives in Mueang Chiang Rai District, says her family stopped drinking tap water months ago, once news of heavy‑metal contamination in the Kok broke.
“We still use tap water for daily things. Washing our face, brushing our teeth, watering plants, bathing the pets. The only thing we do not use it for is drinking. We know the authorities have tried to explain. People come out, drink the water on camera, and wash their
