Louis Kigula, a researcher at Drexel University’s Department of Civil, Architectural, and Environmental Engineering (CAEE), has uncovered critical insights into how household-scale water strategies can reshape the environmental and economic calculus of coastal communities battling aging sewer infrastructure. His latest study, published in *Cleaner and Responsible Consumption* (formerly *Cleaner Environmental Systems*), challenges conventional approaches to evaluating carbon emissions in water management, revealing that some solutions long touted for their sustainability may carry hidden trade-offs.
The research builds on a hydraulic model of a high-density coastal neighborhood in New Jersey, where aging combined sewer systems regularly overflow, dumping billions of gallons of untreated wastewater into nearby waterways. Kigula and his team applied life cycle assessment (LCA) to three circular water strategies: rainwater harvesting (RWH), greywater reuse (GWR), and high-efficiency fixtures (HEF). What sets this study apart is its novel functional unit—normalizing carbon emissions not just against water volume or energy use, but against the very problem these strategies aim to solve: combined sewer overflow (CSO) and flooding.
“Most studies look at carbon payback in isolation,” Kigula explains. “But when we measured emissions relative to the actual environmental benefit—reducing CSO and flood volumes—we found that rankings shift dramatically.” For instance, while rainwater harvesting excels at reducing stormwater volume, its carbon footprint per million liters (ML) of CSO prevented is significantly higher than greywater reuse, which offers net carbon savings of −158 kg CO₂-eq/ML. High-efficiency fixtures, though beneficial, lag behind in carbon efficiency compared to the other strategies.
The implications for utilities, municipalities, and energy providers are significant. As climate change intensifies rainfall and urban flooding, the study suggests that a one-size-fits-all approach won’t suffice. “Greywater reuse emerges as the clear carbon winner,” Kigula notes, “but the combined strategy—integrating all three approaches—offers the best resilience under worsening climate conditions.” Notably, the carbon efficiency of the combined strategy improves as climate stress increases, making it a future-proof investment.
For the energy sector, this research underscores a critical point: water and energy systems are inextricably linked. Strategies that reduce CSO and flooding can also lower the energy burden of wastewater treatment, indirectly cutting emissions tied to power consumption. Utilities investing in decentralized water solutions may find that their carbon reduction goals align more closely with operational efficiency than previously assumed.
The study’s findings challenge engineers and policymakers to rethink how they evaluate water infrastructure projects. “We can’t just ask, ‘Does it save water?’ or ‘Does it cut energy use?’” Kigula says. “We need to ask, ‘Does it deliver the environmental benefit we’re paying for—and at what cost?’” This shift in perspective could accelerate the adoption of greywater reuse systems, which currently face regulatory and public perception hurdles, despite their strong environmental performance.
As coastal communities grapple with aging infrastructure and tightening environmental regulations, Kigula’s work suggests that the most effective solutions may lie not in grand engineering feats, but in the careful integration of small-scale, circular water strategies. The question now is whether utilities, regulators, and investors will heed the data—and act before the next storm overwhelms their systems.