Safer than Tap?
We often assume that bottled water is cleaner than tap water, and in some parts of the world, that is certainly the case. In the U.S., bottled water and drinking water contaminant regulations have been harmonized, so drinking water and bottled water should be of the same quality; however, inadequate regulations or regulations that are not well enforced can lead to lower bottled water standards than in developing countries.
Water testing is critical to ensuring quality. Even though standards have been set and initial quality documented, for bottled water, production upsets can have unexpected consequences. For example, a famous bottled water was recalled after benzene was unexpectedly detected, and a recent report found that 10% of bottled water in Shanghai, China does not meet sanitary standards.
Water is analyzed for three broad classes of contaminants: microbiological, organic and inorganic. Inorganic contaminants include metals such as lead (Pb) and cadmium (Cd) that are clearly toxic. Metals such as selenium (Se) may be beneficial antioxidants at low levels, but toxic at higher concentrations. U.S.-regulated primary and secondary drinking water inorganic contaminant levels are shown in Table 1.
Bottled water from around the world has been collected and analyzed to compare the inorganic contaminants to those allowed in the U.S. Several analytical techniques are suitable for the measurements, and, in this case, inductively coupled plasma mass spectrometry (ICP-MS) was chosen for speed and detection limits, using U.S. EPA method 200.8. Detection limits 10 times below the concentration where decision-making is required are generally recommended. Consensus methods and EPA methods generally require a number of quality control tests interspersed with samples for analysis to ensure quality data results for these important measurements.
Table 2 shows a variety of bottled water results. The results are below the regulatory limit in all cases. For many elements, the concentration is below the detection limit as measured using the EPA definition. For several bottled water samples, it is interesting to note the presence of uranium. Although it is below the regulatory limit, it is clearly present and can be detected very sensitively by this analytical technique.
Disinfection with ozone, rather than chlorine, is becoming more popular for bottled water because it does not leave a residual smell or taste. Because bottled water is sealed after production, there is less chance than in piped delivery systems that recontamination with bacteria will take place. If bromine is naturally present in the water to be bottled, ozone disinfection will promote the formation of bromate, a carcinogen. Although total bromine can be measured with ICP-MS, it is not possible to tell how much of the bromine is present in the bromate form.
Inorganic speciation is a growing type of analysis, where a separation of the components containing the same element takes place before the elemental measurement. Several of the bottled waters reported previously were also analyzed for bromate using ICP-MS coupled with high-performance liquid chromatography for a separation step before the metal determination. Although the U.S. and Europe regulate bromate at 10 µg/L (ppb), Thai and Chinese bottled water exceeded the limit.
Water analysis is critical to a safe and compliant bottled water supply. Inorganic analysis is an important portion of the analysis and can be performed efficiently using ICP-MS. Measurements should be performed on a regular basis to account for any changes that may have occurred in the source or bottling process.
Speciation measurements are a more recent type of measurement coupling two analytical techniques for the separation and detection of inorganic components. Currently, this can be used for the determination of the disinfection byproduct bromate, and may be further applied in the future as the species of other elements, such as arsenic or selenium, become regulated.