Chiang Rai Villages Warned: Arsenic Makes Kok and Sai Rivers Unsafe

The Thailand Pollution Control Department (PCD) has confirmed that arsenic concentrations in two northern rivers still sit above the national safety ceiling, effectively disqualifying stretches of the Kok and Sai rivers from direct household use until further notice.

Why This Matters

• Unsafe for drinking or cooking – even after boiling.

• Rice paddies and fish cages downstream may absorb contaminants within weeks.

• Fines of up to ฿200,000 apply to local utilities that ignore the ban.

• Free water deliveries are being organised for 46 at-risk villages.

Where the Danger Lies

Laboratory samples from the PCD's 15th survey show arsenic readings of 0.011–0.012 mg/L between the Tha Ton Bridge and the Mithraphap Bridge on the Kok River and 0.011–0.014 mg/L along the entire Sai River corridor in Chiang Rai. Levels remain above the legal threshold of 0.01 mg/L. By contrast, the Ruak River, adjacent tributaries, and the Thai stretch of the Mekong all tested within norms. Officials say seasonal run-off from upstream mining in Myanmar is the likely trigger; heavy autumn rains push mine tailings downstream, and the sediment stays trapped in slower-moving Thai sections long after the flood peaks.

What This Means for Residents

Households that still pump water directly from the Kok or Sai need an immediate plan B:

Tap-water plants in Mae Ai and Mae Sai have switched to deep-well sources; check your latest bill for the notice stamp.

Farm irrigation should rely on stored rainwater where possible; rice can accumulate arsenic in the husk.

Fish farming cages on the two rivers are advised to halt feeding for 72 hours and test flesh samples before sale.

Sub-district clinics are offering free medical screening for pregnant women, children, and the elderly.

Remember, boiling water does not remove arsenic; only household filters labelled “ANSI/NSF 53 arsenic” are effective but need cartridge changes every 6 months.

Government & Local Response

The Thailand Pollution Control Department has issued an Emergency notice to provincial governors. Immediate steps include dispatching municipal tankers to hillside hamlets, opening community workshops on filter maintenance, and activating an online dashboard that maps hourly readings. Bangkok has also revived stalled cross-border negotiations with Naypyidaw to curb upstream mining discharge. Meanwhile, the Interior Ministry is releasing ฿45 M from its environmental fund for rapid-install arsenic filters at six rural schools.

Looking Ahead

Scientists expect some rainy-season dilution, yet warn that accumulated sediment will continue to leach toxins. Long-term fixes under discussion range from dredging heavily silted bends to tightening a proposed green mining code that would bind foreign operators. Local tourism boards fear a reputational risk to eco-tourism, while export agriculture groups lobby for fast remediation to protect their markets. Public budget hearings next quarter will determine how much funding is steered toward river health, and a new legislative watchdog panel has vowed monthly audits of the clean-up drive.

The bottom line: until arsenic drops below the 0.01 mg/L mark, residents along the Kok and Sai must treat the rivers as scenic only—not as taps.