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Laredo officials investigate musty odor in tap water; tests show algal compound in Rio Grande
Summary
City testing found traces of compounds produced by cyanobacteria (MIB/geosmin) in raw river water that can cause taste and odor problems though not a public-health risk. City officials said they will flush lines, replace filter media and evaluate activated-carbon “polishing” to address recurring episodes.
Council members and city staff moved Friday to brief residents and begin technical work after a surge of complaints about a musty, earthy taste and odor in Laredo tap water.
City utility and public-health officials said tests show the odorous compound originates in the Rio Grande and is attributable to algal metabolites (commonly measured as MIB and geosmin). Staff said the levels detected are an aesthetic issue — affecting taste and smell — and not a bacteriological or acute health hazard.
Public-health and utilities staff told the City Council they received several hundred resident reports in June and ran about 250 water samples across the system. The samples taken at river intakes and at treated taps showed measurable MIB/geosmin in the raw water feeding the two treatment plants; treated water samples remained in compliance with Texas Commission on Environmental Quality (TCEQ) and EPA standards for contaminants, staff said.
Utility staff described three immediate measures: targeted flushing of distribution lines and storage tanks, cleaning or replacing long‑aged sand filter media at treatment plants, and further monitoring for MIB and related compounds. As a next step they said they will evaluate installing activated‑carbon polishing (granular or powdered activated carbon) after the final filtration stage — a common treatment used elsewhere to remove taste-and-odor compounds that pass conventional disinfection and sand filtration.
Council members asked for public messaging and a short-term plan with estimated costs and timelines. Staff said flushing produced lower MIB readings in many locations but did not remove the compound systemwide because the measured source is in the river itself — conditions that utilities described as the “perfect storm” for algal blooms: warm temperatures, slow flow and elevated nutrient or organic loads from upstream.
Officials urged residents with questions to consult posted results and clarified that water remains within safety limits. Staff also said they plan to coordinate with upstream partners and monitoring agencies to better track episodes and to return with cost estimates for an activated‑carbon solution and filter replacements.
The council did not take a formal vote; staff were directed to return with a schedule and cost estimate for carbon polishing and filter work and to prepare clear public communications about the finding and the mitigation steps.
