The research team began with a market survey to identify which brands dominated local distribution points, then purchased samples in their original sealed condition in February 2026, transporting them in ice-packed coolers to the laboratory for analysis within 24 hours. This careful handling matters, because the goal was to capture the water exactly as consumers receive it. The eight brands selected represented the products most frequently encountered among vendors, retail shops, and street hawkers, making them a reasonable proxy for what residents of these university town and semi-urban communities actually drink every day. The authors acknowledge a limitation: with logistical constraints limiting the study to eight brands, the results may not capture the full diversity of sachet water on the market.

On the chemical side, the news was mostly reassuring. The pH of the samples ranged from 5.80 to 7.37, spanning mildly acidic to near-neutral conditions, with two brands falling squarely within recommended drinking water ranges. Electrical conductivity varied between 0.20 and 1.20 mS/cm, and total dissolved solids ranged from 100 to 600 parts per million, values consistent with treated or filtered water that has passed through purification steps such as reverse osmosis or demineralization. Turbidity, a measure of suspended particles, stayed low overall, peaking at 1.90 NTU in one sample. Dissolved oxygen, which healthy water bodies and potable supplies typically maintain at robust levels, ranged from 6.10 to 7.20 milligrams per liter across the samples.

Organic pollution indicators told a more nuanced story. Biochemical oxygen demand, chemical oxygen demand, and total oxygen demand, three complementary measures of how much oxygen is consumed by microbes and chemical reactions breaking down organic matter, all reached their highest values in the same sample: 1.80, 8.50, and 11.50 milligrams per liter respectively. That clustering suggests localized contamination or a higher load of biodegradable material in that particular brand. The statistical analysis reinforced this picture, revealing near-perfect positive correlations among the three oxygen demand parameters, and strong negative correlations between dissolved oxygen and both organic load and certain metals, a pattern consistent with microbial respiration depleting oxygen as organic matter decomposes.

The bacteriological results were where the study’s real alarm bells rang. Total heterotrophic bacterial counts, a broad measure of living bacteria in the water, ranged from zero to 110 colony-forming units per milliliter, with one brand exceeding the recommended limit of 100 CFU/ml. Coliform counts, which signal possible fecal contamination, peaked at 6.00 CFU/ml in one sample. The isolates recovered from the water produced the characteristic metallic green sheen on eosin methylene blue agar, appeared as Gram-negative rods under the microscope, and showed the classic biochemical fingerprint of E. coli: positive reactions for indole, methyl red, catalase, and motility, and negative reactions for Voges-Proskauer, citrate utilization, urease, and oxidase tests. Because E. coli lives in the intestinal tracts of humans and warm-blooded animals, its presence in drinking water is a universally recognized indicator of fecal contamination and sanitary lapses somewhere in the production chain, from untreated source water to unhygienic filling equipment or improper storage.

What happened next in the laboratory is what elevates this study from a routine water quality check to a public health warning. Using the Kirby-Bauer disk diffusion method on Mueller-Hinton agar, the researchers exposed the nine E. coli isolates to a panel of eight commercial antibiotics. The good news was limited but real: every isolate remained highly susceptible to ofloxacin, with inhibition zones of 26 to 34 millimeters, and cefoperazone performed well against most isolates. Nitrofurantoin showed selective activity, completely inhibiting some isolates while leaving others untouched. But the resistance side of the ledger was far heavier. Every isolate resisted augmentin, ampicillin, ceftazidime, cefuroxime, and gentamicin, with only slight inhibition against gentamicin in three isolates.

To quantify how alarming this pattern is, the team calculated the Multiple Antibiotic Resistance index, a ratio comparing the number of antibiotics an isolate resists to the number tested. Values above 0.2 are conventionally interpreted as evidence that bacteria originate from environments where antibiotics are frequently present. Every single isolate blew past that threshold, with MAR indices ranging from 0.63 to 0.75, meaning the bacteria shrugged off between 62.5 and 75 percent of the drugs thrown at them. Five isolates resisted six of the eight antibiotics. Such values point to high-risk source environments, the authors note, such as sewage systems, hospital effluents, animal waste runoff, or polluted surface waters, where continuous antibiotic pressure selects for resistant strains. The concern is not only that infections caused by these bacteria would be difficult to treat, but that E. coli serves as a reservoir of resistance genes transferable to other pathogens through horizontal gene transfer, a mechanism the World Health Organization has flagged as central to the global antimicrobial resistance crisis.

Heavy metals, by contrast, were largely a non-issue in these samples. Using atomic absorption spectrophotometry after acid digestion, the researchers measured copper, zinc, lead, nickel, cobalt, iron, and cadmium, finding all concentrations below permissible limits. Lead reached at most 0.006 parts per million and iron at most 0.160 parts per million. Three risk indices confirmed the picture: contamination factors for every metal at every site stayed below 1, the heavy metal pollution index ranged from roughly 1.72 to 2.84, far beneath the critical threshold of 100, and the health risk index, which models non-carcinogenic risk to an adult drinking two liters daily over a lifetime, ranged from 0.159 to 0.220, well below the threshold of 1.0 where concern begins. Interestingly, lead contributed the largest share of the modeled risk despite its low concentration, a reminder of how toxic the metal is even in trace amounts, and of why its very low regulatory reference dose gives it outsized weight in risk calculations.

The study’s central paradox is its most important takeaway. Chemically, the water passed. Microbiologically, it did not, at least not consistently. The authors conclude that while the physicochemical and heavy metal quality of the examined sachet water was generally acceptable, bacterial contamination and multidrug-resistant E. coli pose significant public health concerns. They call for strengthened regulatory monitoring, improved hygienic production practices, routine microbiological screening, proper storage systems, and antimicrobial resistance surveillance. They also outline the road ahead for their own work: future studies will employ membrane filtration, API 20E strips, and molecular identification techniques, with larger sample sizes, repeated seasonal sampling, and a broader range of brands to strengthen the risk assessment. For the residents of Ago-Iwoye, Oru, and the countless communities like them across Nigeria and beyond, the message is uncomfortable but clear: the water that looks clean and costs little may be delivering more than hydration, and the invisible cargo of resistance genes it may carry represents a slow-moving threat that chemical testing alone will never catch.

Subject of Research: Multidrug-resistant Escherichia coli contamination and public health risk assessment of sachet drinking water in southwestern Nigeria

Article Title: Multidrug-resistant Escherichia coli in selected sachet water and associated public health risk assessment in Ago-Iwoye and Oru, Ogun State, Nigeria

Article References: Samson, O. J., Adeyemi, J. O., Okunlola, D. O., Obadina, A. O., Omolade, O. A., Osikoya, O. V., Oliwo, A. A., Adeyemi, O. A., Ogunmoye, A. O., & Onajobi, I. B. (2026). Multidrug-resistant Escherichia coli in selected sachet water and associated public health risk assessment in Ago-Iwoye and Oru, Ogun State, Nigeria. Discover Chemistry, 3(1), Article 523. https://doi.org/10.1007/s44371-026-00975-0

Image Credits: AI Generated

DOI: 10.1007/s44371-026-00975-0

Keywords: Escherichia coli, sachet water, antimicrobial resistance, drinking water quality, Nigeria, water microbiology, heavy metals, public health, MAR index, coliform contamination, Ogun State, risk assessment