Surface Water is Changing. Is Your Treatment Strategy Evolving With It?

Our raw water is getting warmer, flashier, and more chemically complex. The old playbook can't keep up.

During the summer and fall of 2021,a severe cyanobacteria harmful algal bloom in Clear Lake, California, offered a chilling glimpse into our new reality. Microcystin concentrations reached an astonishing 17,000 micrograms per liter in some areas—more than 2,000 times the EPA's recreational safety threshold. The crisis was so persistent that a subsequent CDC study found that 58% of homes drawing tap water from the lake had detectable microcystin levels. The event forced the 18 drinking water utilities relying on the lake into emergency response, with one district securing a $10 million state grant to overhaul its system. This was a stark reminder of a question that keeps many of us in the water industry up at night: Can today’s treatment plants keep pace with tomorrow’s source water?

For decades, we operated on an assumption of relative stability. We built our plants and designed our processes based on a historical range of conditions—a predictable rhythm of seasonal temperatures, turbidity spikes, and raw water chemistry. We knew things varied, of course, but we believed they varied within a knowable, manageable box. I think we have to be honest with ourselves: that box is broken. The stability we relied on is eroding, perhaps faster than we're prepared to admit. Our surface waters—the rivers, lakes, and reservoirs that are the lifeblood of our communities—are changing at an accelerating rate.

This isn't a distant environmental issue; it's an operational reality that impacts budgets, infrastructure, and public trust every single day. It's the taste-and-odor complaint call after a heatwave, the overtime hours spent managing sludge after a flash flood, the difficult conversation with a city council about the need for a multi-million dollar ozone system. This article is a guide for fellow industry professionals on how to get ahead of this moving target. We'll explore the six key trends reshaping our water sources, the evolution of our treatment tactics, and the next wave of technologies that can help us build more resilient systems.

The Six Trends Reshaping Surface Water

The challenges we face are not isolated incidents but interconnected trends. Understanding their drivers and consequences is the first step toward building resilience.

1. Warmer Raw Water

Peak water temperatures in many source waters are climbing, with some regions seeing increases of 2–5 °C. This is a direct consequence of a warming climate, but it's amplified by the loss of cooling shade from riparian vegetation and, in some cases, thermal discharges from power plants. For treatment plants, this isn't a minor nuisance. Warmer water accelerates bacterial growth throughout the distribution system, demanding higher disinfectant doses and increasing the risk of taste-and-odor episodes. It also can reduce the effectiveness of biological treatment steps that are optimized for a cooler temperature range.

2. Flashier Runoff

A warmer atmosphere holds more moisture, leading to more intense, extreme rainfall events. When this rain falls on urbanized landscapes with high percentages of impervious surfaces, the result is "flashy" runoff. We're now seeing turbidity spikes three times higher than historical norms. These sudden, massive influxes of suspended solids, nutrients, and pathogens can overwhelm the capacity of conventional clarification and disinfection processes, forcing plants to reduce flow or risk a compliance violation.

3. Harmful Algal Blooms (HABs)

The proliferation of large, persistent cyanobacterial blooms, or Harmful Algal Blooms (HABs), is one of the most visible signs of change. This trend is fueled by a perfect storm of factors: excess nutrient loading (phosphorus and nitrogen) from agriculture and wastewater, warmer water temperatures that cyanobacteria prefer, and longer periods of thermal stratification in lakes and reservoirs. The result for utilities is a costly battle against algal toxins like microcystin, requiring advanced monitoring and often the addition of powdered activated carbon or advanced oxidation processes like ozone to ensure public safety.

4. Rising NOM & Color

Across North America and Europe, many utilities are observing a steady increase in the amount of Natural Organic Matter (NOM) and color in their raw water, with some reporting UV-254 increases of 30% or more. This isn't due to new pollution, but rather a complex mix of historical and climate-driven factors, including the recovery of forest soils from past acid deposition and longer growing seasons. For treatment, the consequences are direct: higher coagulant doses are needed, which in turn produces more sludge to manage and increases the potential for forming regulated disinfection by-products (DBPs).

5. Flow Reductions & Drought

In many regions, particularly the American West, climate change is manifesting as reduced water availability. Earlier snowmelt, diminished mountain snowpack, and higher rates of evapotranspiration are leading to significant drops in summer base-flows—in some cases by 20% or more. This not only stresses limited water supplies but also concentrates salts and pollutants in the remaining flow, making them more difficult and expensive to treat.

6. Emerging Contaminants

Finally, our ability to find what we're looking for has outpaced our ability to easily remove it. Advances in analytical chemistry allow us to detect a vast array of synthetic chemicals at the parts-per-trillion level. This includes the now-infamous Per- and Polyfluoroalkyl Substances (PFAS), as well as pharmaceuticals, personal care products, and microplastics. These contaminants challenge conventional treatment barriers, often requiring advanced solutions like granular activated carbon, ion-exchange, or high-pressure membranes.

Why Utilities Feel the Heat

These physical and chemical shifts aren't abstract environmental trends; they translate directly into tangible operational, financial, and reputational pressures that land on the desks of utility managers every day.r triggers, aquifer storage & recovery (ASR) to bank winter flows, pipe network optimisation to maintain water quality under low flows.

• Escalating O&M Costs: This is the most immediate pain point. When a storm brings in a high-turbidity pulse, coagulant doses (like alum or ferric chloride) have to be increased, which is a direct hit to the chemical budget. When a HAB develops, the powdered activated carbon (PAC) feed spikes to adsorb the toxins. All those extra chemicals create more sludge, which costs money to dewater, haul, and dispose of. The increased pumping for more frequent filter backwashes drives up the electricity bill. These are not one-time costs; they are becoming the new, more expensive baseline.

• Regulatory Pinches: The goalposts are moving. The EPA's new Maximum Contaminant Levels (MCLs) for several PFAS compounds are a perfect example, turning a previously unmonitored substance into a primary treatment driver. At the same time, rising NOM levels push utilities closer to their limits for disinfection by-products (TTHMs and HAA5s), forcing a difficult balancing act: use enough disinfectant to ensure microbiological safety, but not so much that you violate DBP rules. The compliance window is shrinking.

• Asset Fatigue: Our infrastructure is taking a beating. The abrasive, sand-like solids in flashy runoff act like sandpaper on pump impellers and valve seats, accelerating wear and tear and shortening their effective lifespan. For utilities with membrane filtration, higher solids loading and the increased biological activity from warmer water mean more frequent and aggressive chemical cleanings, which can degrade expensive membrane modules over time. Even concrete structures can be affected by the more aggressive water chemistry associated with some of these events.

• Reputational Risk: In the age of social media, a minor operational issue can become a major public relations crisis in a matter of hours. A taste-and-odor event caused by a small algal bloom might not be a health risk, but a dozen posts on a community Facebook page can trigger a flood of concerned calls and media inquiries before the utility can even issue a formal statement. Every such event, even when handled perfectly, chips away at the public's fundamental trust in the safety and reliability of their tap water—a utility's most valuable and fragile asset.

The Evolution of Utility Tactics: From Bigger to Smarter

Our response to these challenges has evolved significantly over the past three decades, moving from a reactive to a predictive mindset.

---

Key take-aways

1. From reactive to predictive: Historical practice relied on manual adjustments after quality deteriorated; real-time sensing and modelling now allow hour-ahead process changes.

2. From plant-only to watershed focus: Green infrastructure, nutrient trading and septic-to-sewer conversions are often cheaper than upgrading clarifiers or adding membranes.

3. From single-barrier to multi-barrier trains: Modern plants layer physical, chemical and biological steps (e.g., ozone-BAC-UF) tailored to simultaneous threats like HAB toxins and PFAS.

4. From one-parameter compliance to risk-based asset management: Operators track how climate-driven extremes raise chemical use, energy and carbon, influencing long-term capital plans.

These shifts reflect tighter regulations, climate pressure and improved technology—driving utilities to become data-driven risk managers rather than end-of-pipe troubleshooters.

The Tech Horizon: A Glimpse at Next-Wave Solutions

Fortunately, a new generation of technologies is emerging to meet these challenges head-on. Many are moving from the lab to pilot-scale and early adoption, offering a more precise and proactive toolkit.

Targeting Temperature with Surgical Precision

Instead of just accepting warmer water, utilities are starting to use Fiber-optic Distributed Temperature Sensing (DTS). By running a fiber-optic cable along an intake pipe, operators can get a real-time, meter-by-meter temperature map of the entire water column. This is a huge leap from traditional thermistor chains, which only provide data at a few discrete points. Connected to a SCADA system, this allows a utility to dynamically adjust its variable-depth intake to selectively draw water from the coolest, highest-quality layer, avoiding warm, algae-prone surface water or anoxic, iron-rich bottom water.

Outsmarting Storms with Predictive Detention

Conventional stormwater detention basins are static—they fill up, then they drain. But by retrofitting them with IoT-controlled valves and real-time level sensors, they become "smart" detention basins. These systems can integrate with weather radar forecasts to pre-drain the basin ahead of a major storm, maximizing its capacity to capture the highly polluted "first flush" of runoff. This dramatically reduces the peak turbidity and nutrient load that hits the treatment plant, smoothing out operations and reducing chemical demand.

In-Reservoir Defenses Against Algal Blooms

Why wait for algal toxins to reach the plant? New in-reservoir strategies aim to suppress blooms at the source. One approach uses drones equipped with spectral sensors to identify bloom hotspots. This data can then trigger automated, solar-powered barges to dispense a targeted, low dose of hydrogen peroxide, killing the algae locally without treating the entire reservoir. An even more futuristic approach involves deploying photocatalytic floating mats. Coated with materials like titanium dioxide, these mats use sunlight to generate reactive oxygen species that inactivate algal cells on contact, offering a chemical-free suppression method. The question, of course, is whether these can scale effectively for large, multi-hectare reservoirs.

A New Playbook for NOM and Color

For the growing challenge of NOM, conventional coagulation is hitting its limits. Magnetic ballast coagulation (e.g., CoMag) offers an alternative by adding magnetite to the coagulation process. This makes the floc significantly heavier, allowing for rapid settling in compact clarifiers that have a 70% smaller footprint than traditional basins. For an even higher level of removal, low-pressure nanofiltration (NF) membranes are becoming viable. Operating at much lower pressures than reverse osmosis (RO), they can effectively reject NOM and color molecules while allowing hardness ions to pass through, reducing the energy and brine disposal costs that previously made membranes impractical for many utilities.

Building a Resilient Supply Portfolio

On the water supply side, utilities are moving beyond static reservoir management. Forecast-Informed Reservoir Operations (FIRO), pioneered in California at Lake Mendocino, use advanced weather and runoff models to dynamically manage water releases. This allows operators to safely hold more water in reservoirs ahead of a dry period, in some cases adding up to 20% more yield without building new infrastructure. To bank this water, Aquifer Storage & Recovery (ASR) is being enhanced with "well couples" that use directional drilling to create separate injection and extraction wells, minimizing mixing with native groundwater and boosting recovery rates to over 85%.

The Final Barrier: Destroying "Forever Chemicals"

For emerging contaminants like PFAS, the goal is shifting from simple removal to complete destruction. While ion-exchange (IX) resins are effective at capturing PFAS, they leave behind a concentrated brine waste that is difficult to dispose of. A next-generation solution uses supercritical CO₂ to regenerate the IX resin, stripping off the PFAS into a small, highly concentrated waste stream that can then be destroyed. For destruction itself, electro-oxidation cells using boron-doped diamond (BDD) electrodes are a promising final barrier. These cells create powerful hydroxyl radicals that can break the strong carbon-fluorine bond, though their high energy consumption remains a practical challenge to overcome.

The Digital Backbone: Sensors, AI, and Digital Twins

Underpinning many of these solutions is a robust digital infrastructure. The goal is to build a hydraulic-quality co-simulator—a digital twin that merges real-time data from SCADA systems, weather radar, satellite imagery, and cost models. This allows operators to test "what-if" scenarios—like the impact of a 100-year storm or a new industrial discharger—in a virtual environment before making costly capital investments. A medium-sized utility in a recent pilot, for example, used an AI-optimized coagulation model to cut its alum usage by 12%, saving tens of thousands of dollars annually. This is the foundational layer that makes technologies like smart detention basins and dynamic temperature gating possible, turning raw data into optimized, automated action.

Beyond the Plant: Nature-Based & Watershed Strategies

Some of the most effective and, I think, most interesting solutions lie outside the fenceline of the treatment plant. This approach treats the watershed itself as the first stage of treatment, focusing on preventing pollutants from reaching the intake rather than just removing them once they arrive.

• Floodplain Reconnection: For much of the last century, our approach was to channelize rivers and build levees to move water away as quickly as possible. We are now realizing the immense value in doing the opposite. By strategically reconnecting rivers to their historic floodplains, we allow high flows to spread out, slow down, and drop their sediment load naturally. These restored floodplains act as giant, passive filtration systems, removing turbidity and nutrients while simultaneously recharging groundwater and creating valuable habitat.

• Nutrient Trading Markets: Upgrading a treatment plant to remove more nitrogen or phosphorus can cost hundreds of millions of dollars. But what if it were cheaper to pay farmers upstream to implement Best Management Practices (BMPs) like cover crops or buffer strips that achieve the same nutrient reduction? This is the idea behind water quality trading. As famously pioneered to protect the Western Lake Erie Basin, these market-based programs allow a regulated utility to meet its nutrient reduction goals by funding more cost-effective, non-point source reductions elsewhere in the watershed.

• Quantifying Co-Benefits: The real power of these nature-based solutions is that they do more than just improve water quality. A restored floodplain doesn't just reduce turbidity; it sequesters carbon, provides recreational space, and increases biodiversity. Historically, it's been difficult to put a dollar value on these "co-benefits." But new frameworks are emerging that allow utilities to quantify these advantages, making it easier to justify investments in watershed health to regulators and ratepayers, and to attract new sources of funding from conservation groups and carbon markets.

A Decision Framework for Utility Leaders

After reviewing the scale of these challenges, it's easy to feel overwhelmed. But as an industry, we have a long and successful history of rising to meet new public health and environmental mandates. From the passage of the Safe Drinking Water Act to the development of advanced disinfection, we have consistently found ways to innovate and adapt. The current moment is no different. It calls for clear-eyed, strategic leadership, not despair. Navigating this complex landscape requires a new way of thinking, but the work is achievable. A successful strategy will likely involve:

1. Source-to-Tap Risk Mapping: This is the foundational first step. It's a comprehensive assessment of vulnerabilities that moves beyond the treatment plant to include the entire watershed and distribution system. Where are your highest risks for nutrient runoff? Which parts of your distribution system are most vulnerable to temperature-driven bacterial growth? A clear-eyed risk map allows you to focus your limited capital on the problems that matter most. The EPA's Drinking Water Mapping Application to Protect Source Waters (DWMAPS) is an excellent example of the toolset available for this kind of analysis.

2. Triple Bottom Line Evaluation: The best project isn't always the one with the highest financial ROI. We need to evaluate potential investments using a "triple bottom line" that considers their financial, environmental, and social impacts. A nature-based solution like restoring a wetland might have a higher upfront cost than a concrete basin, but when you factor in the co-benefits of flood mitigation, habitat creation, and public recreation, it often emerges as the superior long-term investment for the community.

3. Adaptive Pathways Planning: The future is uncertain, and building a massive plant designed for a worst-case 2050 scenario is a risky bet. An adaptive pathways approach offers a more flexible and pragmatic alternative. This involves building modular capacity in "time slices." You might start by investing in advanced monitoring and a pilot-scale ion-exchange system. As the data on emerging contaminants becomes clearer over the next 5-10 years, you can then make a more informed decision about whether to scale that system up, pivot to a different technology, or invest in upstream source control. It's about making smart, reversible decisions now while keeping your options open for the future.

4. Leveraging New Funding: The financial landscape is also changing. While traditional rate-based funding remains essential, utility leaders must become adept at pursuing new funding streams. This includes actively seeking federal funding through established programs like the Water Infrastructure Finance and Innovation Act (WIFIA) and tapping into grants from programs like the Inflation Reduction Act. Furthermore, it's crucial to understand the shifting priorities signaled by new legislation. For example, the recently passed H.R. 1 creates a complex new environment. As I analyzed in a recent post, it provides massive new funding for traditional storage and conveyance projects while simultaneously cutting support for many of the green infrastructure programs that appeal to climate-conscious investors who purchase Green Bonds. Navigating this landscape means aligning projects with these new federal priorities to maximize funding opportunities.

Conclusion: The Path Forward

The era of predictable source water is over. The challenges are significant, but so are the opportunities for innovation. If our industry has proven anything over the last century, it's that we are defined by our response to the great public health and environmental challenges of the day. This is our generation's challenge.

The utilities that thrive in the coming decades will be those that embrace a new role: not just as treaters of water, but as predictive, resilient stewards of their entire water system. This requires a shift in mindset—from reactive compliance to proactive risk management. It means investing in data, piloting new technologies, and building partnerships that extend far beyond the plant's fenceline. The work is complex, but the mission has never been clearer: to build the resilient water systems that will anchor our communities for the next century.

I'm curious to hear your thoughts.

• Which of these six trends is putting the most pressure on your system?

• What pilot technology are you most keen to trial?

• What’s your biggest hurdle to becoming more resilient—capital, staffing, or data?

Let's discuss it in the comments.