MONDAY, Aug. 3, 2015 (HealthDay News) -- Septic tanks don't prevent fecal bacteria from seeping into rivers and lakes, according to a new study that dispels a widely held belief that they can.
"All along, we have presumed that on-site wastewater disposal systems, such as septic tanks, were working," Joan Rose, a water expert at Michigan State University, said in a university news release.
"But in this study, sample after sample, bacterial concentrations were highest where there were higher numbers of septic systems in the watershed area," she said.
Rose and her colleagues analyzed samples from 64 river systems in Michigan.
The study was published in the Aug. 3 issue of the journal Proceedings of the National Academy of Sciences.
Many areas of the United States rely on septic tanks to dispose of human sewage, including Michigan, Florida and South Carolina, the researchers said. They also noted that resort areas near lakes all across the United States often use septic tanks. Regulations on septic tanks vary by state, the researchers said.
Until now, it was thought that soil worked as a natural treatment system that could filter human sewage, the researchers explained.
"For years we have been seeing the effects of fecal pollution, but we haven't known where it is coming from," Rose said.
She added that the study "has important implications on the understanding of relationships between land use, water quality and human health as we go forward."
The U.S. Geological Survey has more about water quality.