Bottled Water Study: Study Design

Motivation

The bottled water industry has grown at record rates in recent years, with global sales reaching $218B in 2020 and U.S. sales alone at $36B.[1][2] Per capita consumption of bottled water in the US has increased from 27.8 gal/year in 2010 to 45.2 gal/year in 2020, demonstrating the increasing prominence of bottled water in Americans’ everyday lives. There is a widespread perception that bottled water is "pure" and free of contaminants, likely due in large part to misleading marketing, which compounds pre-existing distrust in tap water quality. [3-5] While concern about municipal water supplies is warranted given nationwide exposures to toxic chemicals like PFAS and lead, there is inadequate scientific evidence to suggest that bottled water is always a superior alternative.

Various studies have shown cases where bottled water in the U.S. contained a wide range of contaminants, including bacteria, heavy metals including lead and antimony, arsenic, volatile and semi-volatile organic contaminants, disinfection by-products, radiological elements, microplastics, and many PFAS compounds.[3][5-15] Despite evidence that bottled water is not, in fact, free of contaminants, we know of very few studies that compare bottled water quality directly to tap water quality in the U.S., or that include assessment of the potential health impacts of the consumption of bottled water, and none that do both.

Research Questions

We set out to answer two questions with this study:

1. What is bottled water quality in the California Bay Area?

2. How does bottled water quality compare to tap water quality in the same area?

We are uniquely positioned to make a robust comparison between bottled water quality and tap water quality due to our database of water quality tests of thousands of drinking water samples across the U.S. We chose to focus this study on the California Bay Area in order to assess the true choices available to a specific population. And we centered the potential health impacts of the different water sources in our analyses, rather than just comparing concentrations of contaminants without any indication of the actual effects of exposure.

Methods Summary

We made comparisons between sample sets that were representative of the actual drinking water choices available to residents of the Bay Area. To this end, we carefully selected bottled water samples such that the full sample set is representative of the products people are likely to purchase based on market share data and availability. 

The tap water data we used for comparison was taken by the end users in the same region that bottled water samples were purchased. The large sample size, and the fact that the samples were taken at the tap rather than at treatment plants, gives us confidence that the tap water data creates an accurate picture of drinking water quality across the Bay Area.

We also categorized tap water data into untreated and treated samples to compare against bottled water sample results. The untreated tap water sample set is composed of samples taken directly from people’s taps with no further in-home treatment (beyond the municipal water treatment plant). Treated samples, on the other hand, have undergone further treatment at residences, typically via activated carbon, reverse osmosis, or other multi-stage point-of-use or point-of-entry systems. By comparing bottled water to untreated and treated tap water separately, we generate a more granular and realistic view of the options people have when choosing their drinking water sources.

In order to assess the potential health impacts of the analytes measured, we compared concentrations of contaminants known to have adverse health impacts to health-based benchmarks calculated by reputable public health and governmental agencies. These benchmarks are set at concentrations that are protective of human health with respect to cancer and/or non-cancer impacts. The most conservative (lowest) health-based benchmark for each contaminant was used in our data analysis. We did the same type of analysis for aesthetic effects – aesthetic-based benchmarks were set at the lowest concentration of a contaminant at which an aesthetic impact may be perceived, i.e., a taste, odor or color. Concentrations of contaminants with known aesthetic impacts measured in the samples were then compared with the benchmarks.

Full results of the study will be released soon. More details about the bottled water and tap water samples follow.

Bottled Water Samples

We purchased 100 different bottled water products, representing 89 brands, from stores around the San Francisco Bay Area in July of 2022. The products were differentiated by FDA-defined categories based on the water source or further treatment employed: 46 products were classified as “purified” (including 6 products further classified as “distilled” and 9 products that were marketed as “alkaline” but have no official designation beyond “purified”), 46 products were classified as “spring”, “artesian”, “mineral” or “well”, which are grouped together as “groundwater” for the purposes of analysis, and 8 products do not qualify as “bottled water” under FDA regulations and were therefore not regulated as such–these products are referred to as “unregulated” in our analyses.[16]

The categories of bottled water products purchased were informed by the market share of bottled water products sold by category in the U.S. in 2020. In 2020, about 41% of products sold were labeled spring or mineral water, another 41% were purified (including distilled), and the remaining 18% are described as sparkling or other.[1] Sparkling water can fall into any of the regulatory categories, including unregulated, so we kept our groundwater and purified categories approximately equal and allowed for 8% of our samples to be unregulated assuming that around half of the sparkling products sold were unregulated.

In addition, products purchased purposefully included both large and small brands, as well as private labels, so as to represent the various sizes and types of companies that produce bottled water. In order to create a sample set of products that was representative of those available across the San Francisco Bay Area, we first took an inventory of the bottled water products available at 82 stores around the nine county Bay Area region. The final sample set includes at least one product from each location inspected.

Bottled Water Inventory Locations

Each bottled water product was sent, unopened, within one week of purchase, to an accredited environmental testing laboratory for analysis. Samples were tested for 103 analytes in the following categories: general water quality characteristics, non-metal inorganics, metals and metalloids, disinfection byproducts, petroleum compounds, other volatile organic compounds, and indicator bacteria. The full list of analytes is included in the Appendix of this document.

Tap Water Samples

The tap water data used in our study is from the analysis of 715 municipal tap water samples taken by residents in the same nine county Bay Area region shown above between 2017 and 2022. Residents purchased Tap Score water testing kits from SimpleLab and were provided with sample containers and instructions regarding appropriate sampling techniques. Samples were then analyzed at accredited environmental testing laboratories around the U.S.

As discussed above, tap water samples were disaggregated based on whether or not they went through additional in-home treatment (we excluded samples from the treated category where there was only a water softener–we did not consider this treatment as it does not affect potential health impacts of the water).

What’s Next

In our next release, we’ll share the results of our bottled water testing by itself. You’ll get detailed information on the quality of bottled water available in the Bay Area and we’ll put the results in context of potential health impacts. The final report we will share will focus on comparing the bottled water quality with tap water quality in the Bay Area, focusing on the potential health impacts of the different drinking water choices available for residents. Stay tuned for the results.