WaterBacteria in tap water traced to the water treatment process

Published 21 August 2012

Most of the bacteria that remain in drinking water when it gets to the tap can be traced to filters used in the water treatment process, rather than to the aquifers or rivers where they originated; the findings could open the door to more sustainable water treatment processes that use fewer chemicals and, as a result, produce lower levels of byproducts that may pose health risks; eventually, the work could enable engineers to control the types of microbes in drinking water to improve human health

Most of the bacteria that remain in drinking water when it gets to the tap can be traced to filters used in the water treatment process, rather than to the aquifers or rivers where they originated, University of Michigan researchers discovered.

Their study — a unique, broad-based look at Ann Arbor’s water supply from source to tap — could open the door to more sustainable water treatment processes that use fewer chemicals and, as a result, produce lower levels of byproducts that may pose health risks. Eventually, the work could enable engineers to control the types of microbes in drinking water to improve human health like “live and active cultures” in yogurt, the researchers say.

A University of Michigan release reports that the research, led by Lutgarde Raskin, a professor of civil and environmental engineering, is published online in Environmental Science & Technology and will appear in a forthcoming print edition.

Over six months, the researchers sampled water at twenty points along its path from groundwater and Barton Pond sources to residents’ faucets and several more places in the water treatment plant. They harvested bacteria from each sample and sequenced their DNA.

Tap water is teeming with bacteria despite the intensive filtering and disinfection that occur in most of the developed world. This is not necessarily a problem, the U-M researchers say. It could be an opportunity.

A major goal right now in drinking water treatment is to kill all bacteria because there’s the perception that all bacteria are bad. But there’s a good bit of scientific literature that says there are good bacteria, innocuous bacteria and bad bacteria. If we can better understand the types of bacteria in the microbial community from source to tap and what processes control it, perhaps we can be more effective at controlling which ones get through,” said Ameet Pinto, a lecturer at the University of Glasgow who worked on this project as a postdoctoral researcher in Raskin’s lab.

Most previous drinking water studies have focused more narrowly on disease-causing pathogens, Pinto said. Bacteria such as Legionella, Salmonella, and E. coli do not exist in isolation.

Their fate is influenced by the microbial community around them.

The more critical questions are ‘Where do they come from?’ and ‘What determines which ones survive treatment and end up in our drinking water?’ These questions have not been systematically asked until now,” Pinto said.

The study found that the “activated carbon filters”

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