Elemental compositions of deionized water and tap water

Quality of water used in experiments is critical for overall experiment success. Deionized water is the de facto water source for many experiments in science ranging from chemistry to biology. However, there are few reports of elemental composition of deionized water and tap water in the literature. In this short report, the elemental composition of deionized water and tap water from a laboratory was determined by inductively coupled plasma mass spectrometry (ICP-MS). Results indicated that concentrations of various elements in both deionized water and tap water were in the parts per billion (ppb) range, except for sodium, potassium, calcium and magnesium in the low parts per million level. One perplexing finding was that the cation concentrations of deionized water was not significantly lower than that of tap water. This could be due to reduced ion exchange capacity of the ion exchange resins in the deionized water production system, that result from blockage of pores of the resins from particles not removed by the filtration system. Overall, the results highlight the importance of regular maintenance in ensuring production of good quality deionized water from a deionized water production system.