Septic tanks are supposed to break down fecal waste to prevent E.coli and other harmful pathogens from entering the environment, particularly freshwater systems. However, a new study has revealed that this is not the case.

The study conducted by Michigan State University water scientist, Joan Rose, together with her team of fellow water detectives, showed that US rivers and lakes are being contaminated with pollutants seeping from septic tank systems.

The study, which was published online in the August edition of the Proceedings of the National Academy of Sciences, is the largest study ever conducted on watersheds, and serves as a benchmark for assessing water quality and the impact that septic sewage systems have on freshwater systems, and the implications to both the environment and human health.

"All along, we have presumed that on-site wastewater disposal systems, such as septic tanks, were working," said Rose, Homer Nowlin Chair in water research. "But in this study, sample after sample, bacterial concentrations were highest where there were higher numbers of septic systems in the watershed area."

Conventional wisdom has led us to believe that microbes in the soil break down human waste and that soil particles serve as natural filters, removing contaminants from the wastewater as it seeps through. Soak-away septic systems such as a pit dug in soil below an outhouse or a septic tank that discharges out to a drainage field have been in use for centuries. However, according to Rose, these treatment methods fail to keep harmful pathogens such as E. coli from entering freshwater systems that supply us with drinking water.

"For years we have been seeing the effects of fecal pollution, but we haven't known where it is coming from," she said. "Pollution sources scattered in an area - called non-point - have historically been a significant challenge in managing water quality."

The research team used a novel method akin to that used by Crime Scene Investigation (CSI) detectives -- aptly named "CSI for water" by Rose -- to assess water samples from 64 Michigan river systems for traces of 2 human fecal bacterial contaminants: E. coli and B-theta, and to track the origins of these non-point pollutants back to their source.

Many states across the US, including Michigan, South Carolina and Florida, depend on septic tanks for the treatment of human waste, as do most lake resorts and resort towns located near lakes across the country. While the regulations for septic tank wastewater management differ from state to state, stricter measures need to be enforced to ensure freshwater systems are not contaminated as a result of septic tank seepage.

"This study has important implications on the understanding of relationships between land use, water quality and human health as we go forward," Rose emphasized. "Better methods will improve management decisions for locating, constructing and maintaining on-site wastewater treatment systems. It's financially imperative that we get it right."

Considering the health hazards posed by bacterial contamination of our drinking water sources, consumers are encouraged to take measures to protect their health and that of their family by investing in a good quality home drinking water filter that is capable of removing bacteria such as E. coli as well as other contaminants that are commonly found in drinking water.

Journal Reference

Marc P. Verhougstraete, S.L Martin, A.D. Kendall, D.W. Hyndman & J.B. Rose. Linking fecal bacteria in rivers to landscape, geochemical, and hydrologic factors and sources at the basin scale. PNAS, August 2015. doi: 10.1073/pnas.1415836112