Detection of public health concerns occurred only after human consumption of toxic public tap water in Flint, Toledo, and Charleston in recent years. These events demonstrate a need for improvement of water quality monitoring frameworks. We are evaluating low-cost approaches to water analysis that harness the coffee-ring effect. The coffee-ring effect is the phenomenon by which water droplets leave distinguishable “fingerprint” residue patterns after water evaporates, reflecting the solubility and size of chemical constituents. Droplets of various tap water samples were dried on low-cost aluminum substrates and photographs of the residue patterns produced by the coffee ring effect were photographed with a cell phone camera through a $18 jeweler’s loupe. Reproducible residue patterns were obtained for tap waters from communities across southern Michigan supplied by groundwater sources. Synthetic tap water solutions were created to mimic community tap waters with varied amounts of hardness, alkalinity, sodium, chloride, sulfate, total dissolved solids, iron, and copper. Features of the residue patterns that correlated to concentration were identified for each tap water component. The coffee-ring effect was also partnered with in-syringe solid-phase extraction to concentrate heavy metals before analysis. Methods were ultimately applied by three groups of minimally trained students to evaluate the data quality achieved by new users and the potential of the method for open-access water testing. Data suggests the coffee-ring effect will be a valuable tool for laboratory tap water analyses, citizen science programs, and hands on tap water education.

Low-cost tap water monitoring via the coffee-ring effect

254th National Meeting (2017)

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