What’s in Your Bottled Water? Look at the Label!

People are drinking bottled water at an increased rate every year. All bottled waters contain inorganic compounds and trace elements that depend on the type of water and regions of origin. The labels of bottled water provide the data necessary to take a closer look at their chemical composition and evaluate the accuracy of the reported results. In the interest of bringing chemistry concepts into the everyday life aspects of our students we have developed a classroom activity where students analyze ingredient labels of commercial bottled waters and compare their results to the data provided by the manufacturer. Students use chemical composition data from the labels of commercially available bottled water to determine if the total concentration of cations, anions, and silica matches the stated total dissolved solids, TDS, (or dry residue). Taking into account stoichiometric considerations, the law of conservation of mass, and the fact that waters are heated at 180 °C during the determination of the TDS, the accuracy of the manufacturer information can be evaluated. In addition, electrical neutrality is evaluated when students convert the content composition given in mg/L to mmol/L and calculate the positive versus negative charges. As an extension to this classroom activity a laboratory exercise is suggested as well. By bringing tangible chemistry examples into the classroom we provide an opportunity for students to apply chemistry to familiar compounds and products in hopes that they will appreciate chemistry more, will be motivated to study concepts in greater detail, and connect the relevance of chemistry to everyday lives.