Univ. of Texas study shows Galvalume preferred for domestic rainwater harvesting uses

By Jerry Heininger, environmental products coordinator, Englert Inc.

For nearly a decade, the Texas Water Development Board has suggested a standing seam metal roof is the most suitable type of roofing material for collecting rainwater for indoor domestic use. But, not until now, however, has that broad scientific contention been supported by an in-depth study.

Heininger, Englert

Jerry Heininger, Englert, Inc.

The issue of water conservation and rainwater harvesting has been fairly widespread in Texas, where people are simply running out of water in rural areas. Consequently they and the Water Development Board have long been interested in the topic of conserving water supplies.

The U.S. Environmental Protection Agency does  not regulate the quality of residential rainwater collected through harvesting, but some local agencies and states, like Texas and Hawaii — which are among the most proactive –  have long suggested water quality guidelines involving roof materials but have always made it clear the suggestions were not scientifically substantiated.

According to the TWDB, “a renewed interest in this time-honored approach of collecting water has emerged in Texas and elsewhere because of escalating environmental and economic costs of providing water by centralized water systems or by well drilling. The health benefits of rainwater, and potential cost savings associated with rainwater collection systems have further spurred this interest.”

However, the TWDB didn’t have a good, science-based answer about roofing materials until the Cockrell School of Engineering at the University of Texas at Austin launched a detailed study into the issue.

With funding from TWDB, Cockrell School faculty and students conducted an in-depth study — recently published in the academic journal Water Research — examining the effects of conventional and alternative roofing materials on the quality of harvested rainwater.

According to Cockrell sources, the study was led by a civil, architectural and environmental engineering assistant professor Mary Jo Kirisits. It showed that, of five roofing materials tested, “metal (specifically Galvalume), concrete tile and cool roofs produce the highest harvested rainwater quality for indoor domestic use.”

Over the course of a year, Kirisits, her co-principal investigators professor Kerry Kinney and research associate professor Michael Barrett and their engineering students reportedly examined water collected from five roofing materials: asphalt fiberglass shingle, Galvalume, concrete tile, cool and green roofs.

The test sites reportedly included both pilot-scale and full-scale residential roofs — including the roof on Kirisits’ home. Other roofs were located at or near the Lady Bird Johnson Wildflower Center in Austin, Texas.   

The study also showed that “rainwater from asphalt fiberglass shingle roofs and increasingly popular “green” roofs contain high levels of dissolved organic carbon (DOC),” and noted “Although other potential pollutants can be significantly lower on green roofs (turbidity and aluminum), the high DOCs are significant where these roofs would be used for potable rainwater collection.”

According to a statement released by Cockrell, water with DOC is not necessarily dangerous on its own. But, notes Kirisits, when it’s mixed with chlorine — a common product used to disinfect water — the two substances react to form byproducts that potentially cause cancer and other negative human health effects.

According to the report from Cockrell, Kiritis notes “someone who already has a rainwater system is probably not going to change their roofing material based on this study, but this information is useful for anyone who’s trying to make an informed decision about what material to use.”

While some roofing materials performed better than others in the study, Kirisits reportedly noted that rainwater harvested from each of the roofs would still have to be treated if the consumer wanted to meet EPA’s drinking water standards or reuse guidelines.

Heininger is the environmental products coordinator at Englert Inc., Perth Amboy, N.J.

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