Engineering for Pathogen Prevention in a Post-Efficiency Era

By Michael Warady

Imagine a newly expanded municipal service area — complete with state-of-the-art SCADA systems, pressure-zoned districts, energy-efficient pumps and upgraded mainline materials. The project was hailed as a sustainability success: reduced energy consumption, lower water loss and optimized distribution performance. But within a year, localized water quality complaints begin to surface. Traces of Legionella are detected in one of the system’s peripheral zones, despite the presence of proper disinfectant residuals at the treatment plant. How is that possible?

This scenario is becoming increasingly common. As municipalities modernize aging infrastructure and push for conservation, they’re unintentionally creating conditions that foster microbial growth. In many cases, the issue isn’t the water treatment process — it’s how the water behaves after treatment, as it moves (or doesn’t move) through distribution networks designed for a very different era.

When Efficiency Introduces New Risks

Over the last two decades, water utilities have made enormous strides in improving efficiency and compliance. Conservation mandates, pressure optimization and demand-reduction programs have lowered per capita usage across the country. However, these same initiatives often result in increased water age — a condition where water lingers in pipes and tanks far longer than intended.

Low-demand zones, oversized mains, and underutilized storage tanks can all contribute to stagnant conditions where residual disinfectants degrade over time. Add in seasonal usage variability or dead-end mains, and utilities are left with pockets in the system where microbial risks escalate, especially during warm months.

While treatment plants are still performing to spec, the distribution system itself can become the weakest link. Legionella, Pseudomonas and other opportunistic pathogens don’t need to be introduced from external contamination — they can develop within the very infrastructure intended to deliver safe water.

In 2024, a midsize utility in the Midwest began receiving odor and taste complaints from residents in its northern service district. Subsequent testing revealed Legionella pneumophila in a neighborhood with recent water demand reductions due to aggressive conservation rebates and declining population density. Although chlorine residuals at the main treatment plant were stable, water age in certain loops exceeded seven days. The root cause wasn’t a treatment failure — it was a distribution design misaligned with actual use patterns.

Engineering for Resilience in Existing Systems

Unlike new builds, most municipal water systems don’t have the luxury of starting from scratch. Retrofitting existing infrastructure to minimize microbial risk requires utilities to think differently — moving beyond compliance metrics and toward risk-based hydraulic management.

The first step is identifying where stagnation is likely to occur. Even in systems that meet federal and state water quality standards, dead-end mains, undersized loops, and under-circulated storage tanks can serve as unmonitored incubators for biofilm and bacteria. Unfortunately, these vulnerabilities often remain invisible until complaints or outbreaks emerge.

Mitigation doesn’t always require capital-intensive solutions. Some of the most effective interventions are targeted and tactical:

• Looping dead-end mains or installing automatic flushing stations in low-use areas.
• Adding tank mixing systems to prevent thermal stratification and reduce water age.
• Adjusting pump schedules or modulating booster chlorination based on real-time residual data.
• Incorporating flow modeling to redesign zones with declining demand or shifting land use patterns.

In the case of the Midwestern utility, deploying smart flushing valves and recalibrating storage tank turnover schedules reduced water age in the problem area by 60% — bringing microbial indicators back within acceptable levels without any major infrastructure overhaul.

Redefining Water System Success

As utilities grapple with aging assets, regulatory pressures, and public health concerns, there’s a growing recognition that microbial stability must become a core design parameter — not just an operational afterthought.

That shift requires utility leaders to adopt a broader definition of system performance. Rather than simply tracking chlorine residuals or turbidity at the plant, they must ask:

• Is water circulating effectively throughout all zones?
• Are storage volumes sized for actual — not theoretical — demand?
• Do conservation gains unintentionally increase pathogen risk?

Fortunately, emerging tools are making this transition more feasible. Advanced metering infrastructure (AMI) and real-time water quality sensors now allow utilities to identify and respond to stagnation zones dynamically. AI-driven hydraulic modeling can simulate the impact of demand changes and system modifications before they’re implemented. And cross-sector partnerships — with public health agencies, academic researchers, and technology providers — are helping to rewrite the playbook for microbial risk management.

Planning for a Health-Safe Future

The municipal water systems of tomorrow must do more than deliver water efficiently — they must deliver it safely, across every point in the distribution network. That means incorporating pathogen prevention directly into master planning documents, CIP frameworks, and asset management programs.

Utility executives, engineers, and municipal planners all have a role to play. By embedding microbial safety into pipe replacement schedules, tank upgrade criteria, and even land use forecasting, cities can proactively reduce risk long before outbreaks occur.

Just as energy efficiency became a defining metric of infrastructure performance in the early 2000s, pathogen prevention is emerging as the next frontier of utility design and operations. And like energy efficiency, it will require a combination of engineering ingenuity, policy reform, and a willingness to challenge outdated assumptions.

Because in the end, the true mark of a resilient water system isn’t how well it conserves resources — but how reliably it protects public health.

Michael Warady leads Sylmar Group’s industrial water treatment platform as the CEO of Economic Alternatives, Inc. and its affiliated companies. Prior to founding Sylmar Group, he led the infrastructure project development team at AquaTECTURE LLC, a family office investing in and developing innovative water infrastructure projects such as seawater desalination and wastewater reuse.