What's in Your Water
EPA researchers are developing a library of natural organic matter samples to support and advance drinking water research.
Fall has arrived. Time for Thanksgiving, daylight saving time, soccer games, and—leaves. While millions of people enjoy the annual display as entire forests change from dark green to a palette of brilliant yellow, blazing red, and perhaps a million different shades of orange, they might be less welcome if that transition led to an influx of decaying leaves discoloring their tap water dark and making it smell like a pungent pond.
The same forested watersheds and other natural areas that serve as the geographic sources for municipal water supplies are also the source of naturally-occurring materials, from decaying leaves to a host other sources, that can affect the quality of drinking water. These materials, what water quality professionals refer to as “natural organic matter,” or NOM for short, are part of what water treatment facilities target for removal before water is sent flowing into the drinking water supply.
Researchers at EPA are developing a library of NOM samples to support and advance drinking water research. The impact is expected to be significant across the industry, helping to advance filtration and treatment options, processes for reducing disinfection byproducts, and a better understanding of how climate change affects drinking water quality.
NOM offers a number of challenges to water treatment facilities. First, as made evident every fall, the quantity and source of materials that dissolve across the watershed and contribute to natural organic materials entering water sources can change over time.
Another important consideration, particularly for scientists and engineers at EPA, is that NOM has been found to interact with chlorine and other chemicals used to remove pathogens from water, contributing to the presence of disinfection byproducts (DBPs). Concern over the presence of DBPs in drinking water and their potential to adversely affect people has become a concern. As a result, EPA enforces regulatory limits for two primary groups of DBPs linked to health risks, trihalomethanes (TTHM) and haloacetic acids (HAA5).
Some of the same things that make natural organic materials a challenge for water treatment operations—large variations over time as well as significant differences from one location to the next—also make them difficult to study. For example, water treatment engineers and other researchers who want to test and compare new treatment technologies need to ship large quantities of sample water to their laboratories, and expensive proposition.
“The library is envisioned as a repository of freeze-dried samples of natural organic material collected from drinking water sources in different places and at different times of the year. The samples will provide standardized NOM available to researchers and engineers for studying drinking water treatment,” explains EPA environmental engineer Jonathan G. Pressman, Ph.D.
One innovative solution Pressman and his partners have developed is the same one used to feed astronauts and backpackers: freeze-drying. Pressman and his partners have demonstrated that water samples can be freeze-dried and reconstituted without losing NOM or changing its composition. From a sample of 3,000 liters (the equivalent of about 10 bathtubs) of typical filtered and treated drinking water, the researchers are able to produce 10 grams of NOM (the weight of 10 paperclips.)
In the future, EPA plans to develop a NOM library of freeze-dried samples from drinking water sources all around the country. The freeze-dried NOM can be used to make concentrated samples of DBP mixtures, which will advance efforts to identify chemicals too low to be detected in drinking water, facilitating the development of effective engineering solutions and risk reduction strategies. Once NOM is isolated and freeze-dried into a shelf-stable dried powder, it can be reconstituted back into its source water and be used in repeatable experiments. A library of different waters will enable researchers to easily test different water treatment processes on different water sources.