What Climate Change Means for the Next 75 Years of Water Quality

This is part one of a three-part series on climate change. Parts two and three will share solutions to climate-driven harmful algal blooms, disinfection byproduct challenges, and other water quality changes from the perspectives of our utility partners.

At a Glance

• Climate change is exacerbating existing water quality issues and pushing them into new regions, from warming reservoirs to post-flood sediment spikes to algal blooms where they’ve rarely appeared before.

• For over two decades, Hazen’s applied research group has tracked these risks, moving from foundational studies on extreme weather impacts to new projects driven by advanced data tools and holistic approaches. 

• All of that work has the same core focus: giving utilities the context they need to make defensible, data-driven decisions in an uncertain future.  

“We’re working on something that’s happening right now.”

October 2024 was a month when climate research and climate realities collided for Hazen’s Phoebe Aron.

That month, Aron, a hydrologist and climatologist, helped Hazen submit a study of wildfire risks in the Northeastern U.S. That isn’t a region people typically associate with large fires.

But climate change is transforming every region's definition of typical, and a water provider in the Northeast wanted to know: What could climate change mean for wildfires there, and what risks could such fires introduce to its drinking water?

Climate Change Amplifies Existing Water Quality Risks

Climate change often exacerbates weather events that already posed water quality risks.It can also drive back-to-back events that compound each other. Here are a few examples of those risks—wildfires, storms, and algal blooms—and the impacts they can trigger. Click on each icon to learn more.

Two weeks later, Aron’s contact at the utility told her a wildfire had been reported in the region. Soon, fires were burning from northern New Jersey to Massachusetts. Amid record-breaking heat and droughts, it was one of the most intense fire seasons the Northeast had seen in years.

But the utility didn’t panic: Hazen’s research, and the utility’s on-the-ground expertise, showed that while warm, dry conditions could prime the region for wildfires, even in an unusual fire season, the risks to its drinking water systems were typically low. It was able to address the immediate problems and respond with the right level of effort.

Water providers across the continent are raising similar questions amid warmer winters, longer droughts, more intense fires, heavier floods, and other extremes intensifying under climate change. Their questions aren’t just about water quantity: These events can unleash significant risks to water quality that utility managers need to consider.

But Aron said Hazen, which just reached its 75th anniversary, has decades of experience addressing the kinds of water quality risks that climate change is driving. With an applied research program that continues to expand that foundation of knowledge, and increasingly sophisticated data collection and holistic planning tools, she said she’s confident that Hazen—and the industry writ large—can help utilities create the systems they need to keep providing safe, reliable drinking water.

Here’s what’s important to understand about water quality in the context of climate change, from Aron and other top experts at Hazen. 

Climate change is a risk multiplier. But we’ve been helping utilities tackle many of these risks for decades.

Drinking water questions like the one Aron helped the Northeastern utility answer have defined Hazen Vice President Bill Becker’s career.

In the early ‘80s, he towed a rowboat to a remote lake in the Adirondacks every month to study how acid rain was changing the lake’s water chemistry. (In winter, when boats weren’t an option, he’d walk out over the ice with an auger.) A decade later, in one of his environmental engineering PhD classes, his advisor showed a plot of rising global atmospheric carbon dioxide levels and asked what it meant for drinking water.

Becker brought that question, and his ideas on solutions, to Hazen in the early 2000s. As he was starting the firm’s applied research program, one of the first projects he worked on with Hazen’s Ben Stanford and Ben Wright was a Water Research Foundation study of the impacts of extreme weather on drinking water quality.

“Twenty years ago, most of the talk on climate change was on water supply,” said Becker, who serves on the EPA’s Science Advisory Board and recently received AWWA’s prestigious A.P. Black Research Award. 

The team surveyed dozens of utilities across the U.S. and Australia. Many reported gradual, baseline shifts, such as levels of organic matter in reservoirs climbing amid warmer temperatures. Other changes happened suddenly, such as spikes in turbidity after floods and wildfires. Often, utilities experienced multiple weather extremes back to back in ways that compounded the impacts.

These changes strained drinking water systems designed for milder, more predictable conditions. Just thinking about impacts in the Northeast, Becker said, “Some utilities that didn’t used to have to filter their water have installed filtration plants, some of those that had direct filtration have added clarification processes like dissolved air flotation (DAF), and some plants are adding advanced treatment systems like ozone or granular activated carbon.”

But both he and Hazen Director of Water Resources Innovations Josh Weiss said that most of these water quality issues aren’t new. Climate change is just pushing them into new regions or intensifying them where they already exist.

“Climate change takes your existing challenges and multiplies them,” said Weiss, who helps coordinate holistic solutions to these challenges that bridge water resources planning and drinking water treatment. “It makes it more difficult to deal with things that we already have to deal with.”

Becker has helped utilities of all sizes—from less than 5 million gallons per day to more than 2 billion gallons per day—combat water quality challenges associated with climate change. 

“Bill has been working at the nexus of academics and practice for decades,” said Hazen Drinking Water Practice Lead Erik Rosenfeldt. “He’s spent years researching how climate change is causing changes in natural organic matter (NOM) concentrations and understanding how that impacts water treatment.”

When Becker gets a question about dissolved air flotation (DAF) design, he looks to Matt Valade, who “knows the design aspects of DAF better than maybe anyone else in the country,” he said. For harmful algal bloom (HAB) management, he calls Hazen’s Liz Crafton, who studied cyanobacteria for her PhD and has spent more than a decade using that knowledge to help utilities across the country manage complex HAB challenges.

“Hazen’s combination of people who have deep, fundamental understanding of biological and physical-chemical processes and really solid design engineers is what makes us so good at things like climate change,” Becker said. “We understand the fundamentals, and we have the expertise to design whatever’s needed.”

Our applied research keeps expanding our knowledge of these risks—and the solutions available to utilities.

Not every climate-driven water quality risk is well understood yet. When the High Park Fire tore through northern Colorado in 2012, it became one of the most destructive wildfires in the state’s history. It also burned portions of a drinking water utility’s watershed, generating high volumes of ash and runoff, which storms later washed into a key reservoir.

The influx of contaminants took one of the utility’s drinking water plants offline for months, a water quality impact that caught the attention of water experts—including Becker.

On the heels of High Park, he helped Hazen partner with researchers at the University of Colorado Boulder and the Water Research Foundation to study how wildfires can affect drinking water systems, from source water quality to treatment processes to distribution system challenges.

Testing soil and leaf litter from watersheds across the country, the team found that wildfires can dramatically alter water quality (see graphic below for more details), both immediately and in the longer term. 

Wildfire Water Quality Risks

Click on each icon to learn more.

“A lot of times, wildfire runoff has elevated nutrients,” Becker said. “If that water goes into a reservoir, down the road, it’s very possible you’ll have algal blooms that start occurring. How would you handle those? It’s important to think about what happens if you have a fire in a watershed, because the risk is huge.”

Becker and his colleagues also mapped out effective response strategies, from presedimentation basins that capture excess solids to chemical feeds sized for post-fire demand spikes. That kind of information can help utilities design fire-resilient systems and processes well before the next wildfire happens.

We’re using everything from paleoclimatology to remote sensing data to help utilities see “farther” across space and time.

Phoebe Aron flinches whenever she sees reports about temperatures being hotter than they’ve ever been or water quality changing to something that’s never been seen before.

“Those conditions have probably happened before, but not in the recent historical record,” said Aron. “For many of our projects, we have unbelievably detailed hydrologic records from the U.S. Geological Survey.” But she said most of those records go back a century at most. “If we just rely on those records, we’re taking a very narrow look at some of the risks that these systems may face in the future.”

Paleoclimatology, the study of climates predating modern meteorological data, can mine older records written into the earth itself. For example, Aron is part of a Hazen team analyzing tree cores and sediment cores from the Southeastern U.S. to unlock insights into droughts and floods from hundreds, even thousands, of years ago. 

Aron’s team will feed that deep historical data, along with forward-looking projections from international climate datasets like CMIP6, into a Southeastern-area client’s OASIS model to give it a “more representative and robust view of conditions to engineer and design solutions for,” she said.

Josh Weiss said that Hazen is also using remote sensing data to “fill gaps in space and time.” He has led multiple applied research initiatives, including a NASA-funded project, to study how satellite imagery can help identify early indicators of HABs and other water quality changes in reservoirs.

“There are existing platforms that let you zoom into an area on a map and pull satellite data, but they’re all built to see one image at a time,” he said. “We want to know the trends. We want to look at a time series of images and say, if we see this kind of signal today, that gives us good confidence that this bloom is starting to form and could cause a problem in the coming weeks.” 

Holistic approaches can help utilities connect the right information, priorities, and people to make defensible, data-driven decisions.

But broader data only goes so far. Weiss said that given how interconnected these water quality risks are, and how many other risks utilities must balance them against, it’s crucial to address them in a way that reflects the big picture and the bottom line.

He said Hazen, and the broader industry, have shifted from treatment solutions that address individual challenges to holistic approaches that solve multiple problems and create multiple levels of protection—across watersheds and across time horizons. 

A decision support framework Hazen recently created with Halifax Water in Nova Scotia embodies that kind of 360-degree thinking. The framework, developed with Water Research Foundation funding, includes highly technical tools for helping the utility respond to everything from HABs to disinfection byproduct issues. But their development began with human connection, through a series of workshops focused on understanding, and increasing, the ties between the teams that would be using them.

Interdisciplinary thinking powers Hazen’s approach, too. The diversity of skillsets within the water resources team—from Weiss’s data analytics and holistic planning experience to Aron’s climate science and modeling expertise—allows the firm to help utilities consider both water quantity and quality challenges associated with climate change. And “the teams we build to design these holistic solutions draw experts from across different technical and practice groups,” Weiss explained, from hydrologists and drinking water process engineers to GIS specialists and financial analysts. 

We’re in the trenches with you.

Since completing that wildfire risk assessment for the utility in the Northeast, Aron said, her team has moved to helping it add next-generation climate projection capabilities to its hydrologic models. It’s cutting-edge work that’s pushing the capabilities of Hazen’s OASIS modeling tools farther than she’s ever seen them go, to help this water provider protect its supplies for decades to come.

“As a climate scientist, I feel confident saying the next 75 years of water will not look like the past 75 years,” Aron said. “But Hazen is very well versed in helping utilities navigate uncertain decision-making landscapes.”