Total Organic Carbon (TOC) testing is a measurement of the quality of water in a similar way to conductivity. While conductivity looks for dissolved inorganic material the TOC test looks for organic material in most cases are dissolved for Purified Waters. Much of the organic carbon found in natural water are Humic substances which come from dead plants, trees etc. For more purified water TOC can give an indication of the residual presence of cleaning chemicals such as alcohols and peracetic acid.