ERI: Engineering safer rainwater harvesting systems: Relating viable Legionella concentrations to system design and environmental characteristics

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).

As precipitation patterns change due to climate change, there is a critical need to augment potable and non-potable water sources in drought prone areas and reduce stormwater runoff in areas more susceptible to heavy precipitation. Rainwater harvesting has emerged as a promising and sustainable technology to address both of those needs. Harvesting rainwater involves the collection and storage of rain for subsequent usages such as landscape irrigation, vehicle washing, and toilet/urinal flushing.

With the appropriate treatment, harvested rainwater could also be utilized for potable needs including drinking, cooking, and bathing. However, for potable usage, rainwater must be treated to eliminate risks to human health including the complete removal of Legionella, a waterborne pathogen that has been detected in harvested rainwater worldwide. The overarching goal of this project is to advance the implementation of a novel and more effective assay for detecting and quantifying the presence of harmful Legionella bacteria in harvested rainwater.

To advance this goal, the Principal Investigator of this project will explore the use of ethidium monoazide quantitative polymerase chain reaction (EMA-qPCR) as a new and promising assay that could accurately quantify the concentrations of viable and harmful Legionella bacteria in harvested rainwater. The successful completion of this project will benefit society through the collection of new data and development of fundamental knowledge to prevent exposure to harmful Legionella bacteria when using harvested rainwater for potable and non-potable applications.

Further benefits to society will be achieved through student education and training including the mentoring of two undergraduate students at Longwood University.

Legionella is a waterborne pathogen, if inhaled, can cause severe illness in humans. Legionella bacteria have been detected in rainwater harvesting systems (RWHS) worldwide. Culture-based methods cannot detect viable but non-culturable cells and thus they tend to underestimate the concentration of harmful Legionella cells present in a water sample.

Molecular methods such as qPCR cannot distinguish between living, viable, and dead cells and consequently they tend to overestimate the concentration of harmful Legionella bacteria in a water sample. The goal of this ERI project is to advance the implementation of a promising new technique (ethidium monoazide quantitative polymerase chain reaction or EMA-qPCR) that could lead to more accurate estimates of the concentration of viable and harmful Legionella bacteria in harvested rainwater.

To advance this goal, the Principal Investigator will conduct point-of-use sampling at 50 RWHS and measure the concentrations of Legionella bacterial species including harmful L. pneumophila bacteria using four methods including a cell culture-based assay, qPCR, an enzyme-based assay (Legiolert™), and EMA-qPCR. The successful completion of this project has the potential for transformative impact by providing data to support new and more accurate estimates of human health risks associated with the potable and non-potable usages of harvested rainwater.

The fundamental knowledge gained from this project could also enable engineers and communities to design, build, and deploy more effective and safer RWHS to augment potable and non-potable sources of water while reducing surface and groundwater pollution due to stormwater runoff.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.