Not too long ago, a local leader in a community in Nevada asked if I could review a set of water testing data. The sample was taken from a water storage tank that provides drinking water to the town where she lives. The town had painted the inside of the storage tank, but now the water has a strong chemical odor and four volatile chemicals were found in the water sample.

The concentration of all four chemicals in the water was below the federal drinking water standards and as far as the town was concerned, the conversation was over. The water was safe to drink. But is it really? What’s the basis for saying this?

Federal drinking water standards are based on exposure to a single substance in isolation of any other risks and reflect only a limited exposure, typically one day, from a single route of exposure, ingestion. But this is not how people are typically exposed which is to multiple chemicals at the same time. The federal standards do not address the cumulative risks posed by exposure to multiple chemicals over time. Further, these standards fail to address potential synergistic effects which are adverse health effects that are greater than would be predicted or expected based on exposure to individual chemicals alone or in combination.

Consequently, estimating risks posed by exposure to multiple chemicals in drinking water using federal drinking water standards underestimates the true risks people face drinking and using this water on a regular basis. Scientifically, we do not know how much these other factors add to the risks a person faces when drinking water with multiple contaminants. Even though each of the four chemicals in this example were found at concentrations below the federal drinking water standards, this does not mean that there is no risk when consuming or using this water. It does mean that science cannot inform this question.

Yet you hear all time when tests results are interpreted by government agencies that there is no cause for alarm. The standards are used like the proverbial line in the sand. On the one side, people are safe, and on the other, there’s endless debate over what the numbers mean. In truth, it’s not that simple.

In this case, each of the four chemicals found in the water affect the central nervous system and the liver. This means that these organ systems are all targeted simultaneously by each of these four substances. The health impact on the central nervous system (CNS) and the liver resulting from exposure to all four of these substances at the same time is difficult to judge because there is little or no information on exposure to multiple chemicals simultaneously. In addition to these targeted effects on the nervous system and the liver, these chemicals pose other specific health risks whether its skin irritation, the ability of the body to fight infection, or damage to the kidney or the heart. In many cases, some chemicals are considered carcinogens, that is, exposure increases the risk of developing cancer. The EPA’s health goal for exposure to all suspect carcinogens in drinking water is “zero” indicating that any exposure to this substance increases the risk of developing cancer over time. But EPA adjusts the health goal to reflect the realities of setting a drinking water standard at a concentration of “zero.”

In addition, because all these substances are volatile, they will evaporate into the air when a person takes a shower. One study compared the risk posed by taking a 15-minute shower versus normal consumption of drinking water and found that the risk of taking a 15-minute shower was greater than drinking the water (https://www.sciencedirect.com/science/article/pii/0048969785903493?via%3Dihub). This risk is not included the federal drinking water standard.

While the concentration of these substances in the water may be below the federal drinking water standards, there is significant uncertainty about the cumulative risks posed by simultaneous exposure to these four volatile chemicals in drinking water, especially over time.

This is just one example of how difficult it is to interpret the results of water testing. This situation is quite common, whether it’s contaminants in drinking water, chemicals in ambient air or contaminants in soil. Interpreting air and soil testing is even more difficult because there are no federal standards that define what levels are acceptable and what are not. Instead, EPA uses guideline values that are not enforceable and subject to political whims.

CHEJ can you interpret the results of any testing results you’re concerned about. Contact us if you have test results you need help interpreting.