Mae Sai Water Authority Halts Production Due to Arsenic
Arsenic contamination in the Sai River reached 0.25 milligrams per liter—25 times the safety standard of 0.01 milligrams per liter—forcing the Provincial Waterworks Authority branch in Mae Sai to halt water production for a full day. When the water crisis struck, officials expected the disruption to remain brief and localized, but physical tests revealed turbidity levels soaring to 14,000 NTU, exceeding the typical dry-season range of 800 to 1,000 NTU and the flood-period range of 3,000 to 6,000 NTU.
Arsenic Contamination Halts Mae Sai Water Production
The water crisis struck the border district of Mae Sai in Chiang Rai province when regional monitoring revealed heavy metal levels soaring far above acceptable thresholds.
The severe turbidity and chemical load overwhelmed the local water treatment plant’s physical filters. The Provincial Waterworks Authority branch in Mae Sai suspended operations at 5:30 p.m. on November 5, 2026, cutting off treated water supplies until 5:30 p.m. on November 6, 2026. The stoppage left 14 villages across Mae Sai and Wiang Phang Kham subdistricts without normal tap water access, specifically affecting Moo 2, 3, 7, 8, and 10 in Mae Sai subdistrict, and Moo 1, 2, 3, 4, 5, 7, 8, 9, and 10 in Wiang Phang Kham subdistrict.
Families relied on dwindling storage tanks or sought out mountain gravity-fed water lines from neighbors while demanding emergency water truck deployments.
Heavy Rainfall Washes Chemical Residues into Sai River
Officials confirmed that water production had initially been reduced to 60 percent before recovering to 80 percent.
Piyanuch Thuangkham, Director of the Water Quality Management Division at the 1st Regional Environment and Pollution Control Office, noted that contaminants in the Sai River had previously spiked to 28 times the standard in early August before settling into a range of 0.012 to 0.017 milligrams per liter. Officials attributed the acute surge to heavy upstream rainfall washing chemical residues into the river.
To address the recurrent crisis, the Provincial Waterworks Authority outlined a multi-phase infrastructural plan. Short-term relief involves preparing 100-cubic-meter groundwater wells. Medium- and long-term plans focus on piping raw water from the Mekong River via Chiang Saen, tapping reservoirs at Mae Kham and Mae Salab in Mae Fa Luang district, and planning automated water quality monitoring stations along the Sai, Ruak, Kok, and Mekong rivers.
Residents Abandon Wild-Caught Fish Amid Arsenic Findings
The regional water crisis intersects with broader public health findings across northern and northeastern Thailand. Separately, 79 individuals tested positive for inorganic arsenic, the highly toxic form associated with chronic exposure.
Local communities along the Sai and Ruak rivers have largely abandoned consuming wild-caught fish, turning instead to commercially farmed alternatives. Meanwhile, officials and residents continue to push for cross-border diplomatic negotiations regarding upstream mining activities, demanding that environmental regulators provide continuous, verified public safety data rather than spot-check assurances.