Expert Views

Bottled or tap?

by Stephen C. Edberg, Ph.D.

Recent news about banning bottled water in favor of tap water reveals an underlying assumption that there are no health or safety differences between tap and bottled. But the facts tell another story.

In my 25-year history of studying drinking water, I've seen a growing disconnect between what is known by scientists and health agencies and what is communicated to the public on this topic. It is time we talk frankly about our drinking water choices so consumers can make informed decisions. Tap water has the benefit of not requiring a bottle, but has challenges when it comes to delivering assured quality, for various reasons. Bottled water, a sealed food product, offers quality assurance. However, the bottle needs to get recycled at higher rates than they are today.

To put it simply, there are a variety of differences in how the water is sourced, processed and delivered to consumers that account for the disparity in quality assurance between these two drinking water sources.

For example, about 75 percent of sources for municipal tap water typically are surface waters such as lakes, rivers and reservoirs that are proximate to the populations served. This means little choice in quality of the source.

By contrast, bottled spring water sources are naturally more protected by virtue of being underground. Moreover, these sources can be carefully selected based on their quality and quantity.

Overall, tap water undergoes less specialized filter and disinfection treatments than bottled water. The disinfection process typically used for municipal water is added chlorine. This method can produce disinfection by-products, trihalomethanes that at elevated levels are carcinogenic and statistically associated with birth defects.

Tap water's limited filtration and disinfection processes has led the Centers for Disease Control and Prevention (CDC) to state for immuno-compromised populations, "Because you cannot be sure if your tap water is safe, you may wish to avoid tap water, including water or ice from a refrigerator ice-maker, which is made with tap water" and/or "drink bottled water." By contrast, bottled water employs more highly specialized treatment processes. For spring water, these include filtration, microfiltration, ultraviolet light and low concentrations of ozone. For purified bottled waters, which typically begin as tap or well water, these include very effective purification processes, either reverse osmosis or distillation.

The greatest disparity between tap water and bottled water is the distribution system. Tap is delivered through pipes where the most variability in the safety of tap water occurs. On average, a city loses between 18 percent and 44 percent of its water from leaking pipes. These pipes are often in the same trenches as our sewer pipes. It has been shown that even under normal operating conditions, pressure changes in the distribution system can cause environmental intrusion from the outside of the pipe to the inside, allowing sewage contamination to enter drinking water systems. This open distribution system is more vulnerable to contamination.

Bottled water, on the other hand, uses a more controlled process that can avoid external contamination from the source through the bottling process. Moreover, the bottle hygienically seals in the quality.

Researchers at the Environmental Protection Agency have estimated that there were 16.4 million cases of acute gastro-intestinal illness in 2006 associated with tap water contamination. Further, based on recent estimates, federal health officials believe the impacts of water-borne disease outbreaks are under-reported and under-valued. Conversely, the CDC has associated bottled water with less than 10 incidents resulting in possible cases of illness in the past 35 years.

American consumers are entitled to safe drinking water. And we need a broader dialogue addressing the range of drinking water issues to better decision making, more effective regulations and increased infrastructure funding that is desperately needed by public utilities. Only then can Americans be assured of the quality, safety and reliability of one of our most essential and elemental resources.

Stephen C. Edberg is director of the Clinical Microbiology Laboratory of the Yale-New Haven Hospital and professor of Laboratory Medicine, Internal Medicine and Chemical Engineering at Yale University.


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