Figure 6.

Seven real-world samples tested on Device 2—tap water from the lab faucet, rainwater, Mt. Rainier snow, Atlanta snow, Rio Tinto water, sediment samples from Dyngjusandur, and ocean water samples. For device validation, rainwater, Atlanta snowmelt, and Mt. Rainier snowmelt samples were used without dilution, tap water and Dyngjusandur samples were used without dilution first and then diluted 1:1, and Rio Tinto and ocean samples were diluted 1:750 and 1:1500. All real-world sample voltages were plotted against KCl and Na₂SO₄ curves to estimate the total dissolved solid (TDS) content.