It’s no secret that bottled water affects the environment more than tap water, considering the plastic and energy required to produce the bottles (to name just a few downsides). But you’d probably be surprised to see just how much worse it is. Researchers have calculated just that — and it’s a lot.

Bottled water consumption has sharply increased in the last years worldwide, especially in low- and middle-income countries. According to previous studies, this is partly explained by psychology. Bottled water is often perceived as having better taste, odor, and as being more healthy. There’s often a lack of trust in public tap water quality and marketing campaigns by bottled water companies further erode this trust. 

In a new study, researchers from the Universitat Politècnica de Catalunya·BarcelonaTech (UPC) carried out a life cycle assessment to estimate the environmental impact of tap and bottled water. This was done with a specific method that allowed them to estimate the damage to ecosystems and to resource availability as well as indirect impacts to human health.

Since tap water quality may change between cities, the researchers focused on Barcelona due to the robustness of available data. Barcelona is home to around 1.35 million people – nearly 60% of whom consume bottled water at least some of the time. Most bottled water sold in Spain is mineral water, defined as spring water with a constant composition of minerals.

Meanwhile, on the other hand, tap water has improved substantially over the past few years — but people are still skeptical.

“Tap water quality has increased substantially in Barcelona since the incorporation of advanced treatments over the last years. However, this considerable improvement has not been mirrored by an increase in tap water consumption, which suggests that water consumption could be motivated by subjective factors,” Cristina Villanueva, author of the study, said in a statement.

The environmental impact

Let’s put it this way: people’s aversion to tap water, and their implied preference for bottled water, has actual, tangible costs.

If the whole population of Barcelona decided to shift to bottled water, the production required would translate to 1.43 species lost per year and cost of $83.9 million per year due to extraction of raw material, the researchers found. This is 1,400 times more impact in ecosystems and 3,500 times higher cost of resource extraction, compared to the entire population drinking tap water. 

The higher environmental impact of bottled water was attributed to the high input of materials (i.e. packaging) and energy needed for bottled water production as compared to tap water. Indeed, raw materials and energy required for bottle manufacturing accounted for the majority of the impact of bottled water use (up to 90% of the impact in all indicators), consistent with previous studies. 

However, it should also be said that tap water isn’t fully as healthy as bottled water. The researchers also found that a complete shift to tap water would increase the overall number of years of life lost in the city of Barcelona to 309 (which equals approximately on average 2 hours of lost life expectancy if borne equally by all residents of Barcelona). Adding domestic filtration to tap water would reduce that risk considerably.

“Our results show that considering both the environmental and the health effects, tap water is a better option than bottled water, because bottled water generates a wider range of impacts,” Cathryn Tonne, last author of the study, said in a statement. “The use of domestic filters improves the taste and odour of tap water and reduces chemical levels in some cases.”

The study was published in the journal Science of the Total Environment.