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Arthur T Knackerbracket has found the following story:

Homeowners who rely on private wells as their drinking water source can be vulnerable to bacteria, nitrates, and other contaminants that have known human health risks. Because they are not connected to a public drinking water supply, the homeowners are responsible for ensuring that their own drinking water is safe.

Similar to concerns that public drinking water treatment plants face, groundwater wells may be impacted by another group of contaminants—and they might be part of your daily use!

Ingredients in personal care items, over-the-counter and drink products are introduced into domestic wastewater streams and can persist through treatment technologies. "This causes trace-levels of these chemicals to be found in the environment," says Heather Gall. "Recently developed analytical technologies are now advanced enough for us to detect these compounds in water at increasingly low levels." Gall is an assistant professor at Pennsylvania State University who studies contaminants of emerging concern in surface and groundwater.

A fully-functioning septic system releases the effluent slowly into a septic field. The soil, roots, and soil microbes biodegrade pollutants in the water before it gets back into groundwater. However, in the U.S., 10-20% of septic tanks function poorly. This can increase the chance of these contaminants getting to groundwater, especially those that biodegrade slowly in the environment. After that, they can enter a downgradient household's well water.

The presence of medicines in drinking water raise public health concerns. Impacted water may have harmful effects when consumed, but whether the levels present in private wells are high enough to pose a threat is an understudied area of research.

So, Gall partnered with the Pennsylvania Master Well Owner Network. Twenty-six homeowners volunteered to collect water samples from their private wells. "Since our project engaged private well owners, we wanted to focus on compounds they may be familiar with," says Gall.

Gall's team chose to test water samples for four common antibiotics, two over-the-counter anti-inflammatory drugs, and one common stimulant. Each reacts differently with soil in the septic field in different ways. These chemicals can bind physically to soil particles. They also can react with soil, soil microbes, and other compounds in the septic field. It's a virtual chemistry experiment when active pharmaceutical ingredients reach the septic tank.

Gall found that medicines' ability to get to groundwater was mostly controlled by two factors: sorption potential and biodegradability.

Sorption refers to the likelihood of the medicine attaching to another substance like soil or water. Medicines with low sorption are not likely to attach to soil in the septic field. That makes them more likely to move quickly through the soil profile and reach groundwater. The medicine most likely to reach groundwater was ofloxacin. This antibiotic was the most frequently detected medicine in the groundwater samples. Naproxen, an anti-inflammatory drug, had the highest sorption, and was most likely to stay in the septic field. This could be the reason it was not detected in any of the groundwater samples of the study.

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