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WaterOperator.org Blog

Disinfection By-Product Control

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Disinfection kills or inactivates disease-causing organisms in a water supply. Disinfection by-products (DBPs) are formed when disinfectants used in water treatment plants react with bromide and/or natural organic matter, like decaying vegetation, present in the source water to create harmful compounds. Different disinfectants produce different types or amounts of disinfection byproducts.

We have 829 resources (and counting) on Disinfection and Disinfection By-Products in our Documents Database that provide valuable information on this topic. You can search for documents that explain how to use the Drinking Water State Revolving Fund (DWSRF) to address DBPs in drinking water, the basics of ultraviolet disinfection, disinfectant residual control within the distribution system, webinar recordings on ways to simulate disinfectant water chemistry and ways to assess distribution system influent water quality, and many other useful guides that will help you to deliver safe and clean water to utility customers. 

To access the wealth of knowledge on Disinfection and its potential by-products within our database just select "CATEGORY" in the dropdown then choose "Disinfection and Disinfection By-Products." Once you make that selection, a second dropdown will appear where you can choose "HOST," “TYPE,” or “STATE” to narrow the search even further. If you have a specific search term in mind, use the “Keyword Filter” search bar on the right side of the screen.

This is part of our A-Z for Operators series.

Learning Lessons from Supply Chain Disruption

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One of the most prominent economic impacts to emerge from the COVID-19 pandemic was the breakdown of supply chains for many consumer, medical, and industrial products. Though the shortages of goods such as toilet paper, semiconductor chips, personal protective equipment and more made widespread headlines, the range of items affected spread much wider — including to the supply of critical water treatment chemicals. The American Water Works Association found in November 2021 that 45% of surveyed water utilities were experiencing shortages of water treatment chemicals, among other staffing and supply issues. 

Shortages of chlorine did make news in the summers of 2021 and 2022 due to the difficulty pool-owners had obtaining it to clean their pool water, but the threat it posed to water utilities — where chlorine is a critical component of the treatment and disinfection process — was much less widely known. In 2021, the pandemic spurred the shortage by causing a decrease in production capacity, an increase in demand (largely from a boom of newly-installed pools), and other logistical failures. However, non-COVID factors also played a role in the shortages.

Hurricane Laura, which struck Louisiana in August 2020, severely damaged the BioLab Inc. chemical plant, a major US producer of chlorine. In 2022, the labor dispute between rail workers and rail companies briefly led to an embargo on the rail transport of hazardous materials including chlorine and other water treatment chemicals. While further major disruptions did not occur in 2023, the EPA considers the chlorine supply chain to be “vulnerable to periods of reduced product allocation and/or price increases” and maintains a page tracking the status of chlorine availability and pricing. 

The most severe supply chain disruption in 2023 for water treatment chemicals came right at the start of the year — when a four-alarm fire devastated the Carus Chemical factory in LaSalle, Illinois, on January 11. Carus is the only producer of potassium permanganate in North America, which is used to oxidize contaminants in drinking water. While the company initially warned of  a 3-month outage in its production capacity, potassium permanganate production did not resume at Carus until August. Luckily, overseas imports were able to fill demand after some initial shortages, and the EPA found that supply had stabilized by May.

Other water treatment chemical supply chains that the EPA considered to be disrupted since 2020 include carbon dioxide, sodium hydroxide and hypochlorite, hydrochloric acid, ferric and ferrous chloride, oxygen, and fluorosilicic acid. However, none of these disruptions are considered to be ongoing.

While supply chains of water treatment chemicals have always been susceptible to periods of economic strain, such as the Great Recession of 2007-09, COVID-19 revealed many more risks in the system. According to the EPA’s “Understanding Water Treatment Chemical Supply Chains” report:  

“The supply disruptions that have occurred during the pandemic era revealed a range and intensity of supply chains stressors that had not previously been observed in such a short timeframe. While high-impact events such as a pandemic or repeated extreme weather events concentrated on industrial hubs may have been considered low-probability in previous assessments, supply chain risk planning may have to consider greater frequency and co-occurrence of such high-impact events.”

The most prevalent long-standing threats to the stability of supply chains include natural disasters, equipment failures, logistical problems such as transportation delays, and malicious acts like cyberattacks and sabotage — none of which will stop being a concern even as the pandemic is increasingly behind us. International markets can also be severely affected by trade barriers, armed conflicts, and natural disasters. 

Perhaps the most prominent chemical shortage preceding 2020 was a national shortage of chlorine in 1974. While a single cause of the shortage could not be identified, New York Times reporting at the time cited the new requirement to chlorinate wastewater, the closure of production facilities, and the energy crisis of the 1970s (which was peaking with the 1973-74 oil shock) as likely factors.

For more information on the supply chain history of various water treatment chemicals, the EPA’s supply chain profiles of 46 commonly used chemicals contains shortage histories for 2000-2022, as well as risk profiles for shortages of each chemical. Risk ratings for these chemicals can also be found in the “Understanding Water Treatment Chemical Supply Chains” report.

As for future concerns, chlorine availability could continue to be made vulnerable by natural disasters in the Gulf Coast region. 33% of American chlor-alkali facilities, in which most chlorine is produced, are located along the Gulf Coast, which is both historically prone to hurricanes and under greater threat as climate change intensifies storms. Disruptions in chlorine supply also lead to disruptions in ferric chloride supply, which requires hydrochloric acid. 

The EPA has many resources to assist in preparing for and responding to supply chain challenges. The critical steps to prepare are:

  1. Using federal and state support programs for operational efficiency and cost reduction
  2. Management of supplier relationships
  3. Coordinating with other utilities, state and local agencies, and water sector associations
  4. Instituting operational flexibilities 

To respond to disruptions, the EPA recommends:

  1. Seeking federal support
  2. Communicating with suppliers
  3. Coordinating with partners

Follow the Supply Chain Resilience Guide for more information, instructions, and tips to prepare and respond.  

More information, tools, and links from the EPA: 

Arsenic in Drinking Water

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Arsenic is a heavy metal and a regulated contaminant in drinking water and wastewater effluent. In 2001, under the Arsenic Rule, EPA adopted a lower standard for arsenic in drinking water of 10 parts per billion (ppb) which replaced the previous maximum contaminant level (MCL) of 50 ppb. Arsenic is a semi-metal element in the periodic table. It is odorless and tasteless. It can enter drinking water supplies from natural deposits in the earth or from agricultural and industrial practices. 

We have 180 resources (and counting) on Arsenic in our Documents Database that provide valuable information on this topic. You can search for documents about the arsenic rule, complying with the arsenic maximum contaminant level, the reporting requirements for the annual Consumer Confidence Reports (CCR), and many other useful guides that will help you to deliver safe and clean water to utility customers. 

To access the wealth of Arsenic related knowledge within our database just select "CATEGORY" in the dropdown then choose "Arsenic." Once you make that selection, a second dropdown will appear where you can choose "HOST," “TYPE,” or “STATE” to narrow the search even further. If you have a specific search term in mind, use the “Keyword Filter” search bar on the right side of the screen.

This is part of our A-Z for Operators series.

PFAS Treatment: What We Know in 2023

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PFAS (formally known as per- and polyfluoroalkyl substances) are widely used, long lasting chemicals that break down very slowly over time. They break down so slowly that they end up in water, air, fish, and soil all over the world, and trace amounts have even been detected in human blood. Scientific studies have shown that exposure to some PFAS in the environment may be linked to harmful health effects in humans and animals, but we do not know to what extent they may affect us.

PFAS possess chemical properties that mean traditional drinking water treatment technologies are not able to remove them. Researchers have been working on a variety of treatment technologies to determine which methods work best to remove PFAS from drinking water. Some of the most successful methods include: activated carbon adsorption, ion exchange resins, and high-pressure membranes. 

Granular activated carbon (GAC) adsorption: GAC has been shown to effectively remove PFAS from drinking water when it is used in a flow through filter mode after particulates have already been removed. According to EPA researcher Thomas Speth, this method can be extremely effective “depending on the type of carbon used, the depth of the bed of carbon, flow rate of the water, the specific PFAS you need to remove, temperature, and the degree and type of organic matter as well as other contaminants, or constituents, in the water.”

Ion exchange resins: Negatively charged ions of PFAS are attracted to positively charged anion resins. Anion exchange resins (AER) have proved to have a high capacity for many PFAS; but this method can be more expensive than GAC. The most promising version of this method is an AER in a single use mode, followed by incineration of the resin. This technology has no contaminant waste stream to treat or dispose due to the lack of need for resin regeneration.

High-pressure membranes: Research shows that membranes, such as nanofiltration or reverse osmosis, are typically more than 90 percent effective at removing a wide range of PFAS. However, these methods generate a large volume of high-strength waste stream which can be difficult to treat or dispose of for a water system. This technology may be better suited for a homeowner since it would generate a much smaller volume of waste.


PFAS Resources:

  • Drinking Water Treatability Database
    • The Drinking Water Treatability Database (TDB) can be used to identify effective drinking water treatment processes, to plan for future treatment plant upgrades, to provide information to first responders for spills/ emergencies, and to recognize research needs.
  • PFAS Analytic Tools hub
    • This page contains location-specific information related to PFAS manufacture, release, and occurrence in the environment as well as facilities potentially handling PFAS.
  • CWA Analytical Methods for Per- and Polyfluorinated Alkyl Substances (PFAS)
    • This page contains information regarding the EPA’s development of new analytical methods to test for PFAS compounds in wastewater, as well as other environmental media.

Are Solar Powered Water Treatment Plants the Future?

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Clean water and clean energy are both essential on the road to a more sustainable future. To be able to tackle two issues at once and provide clean water using clean energy is exactly the kind of innovation that the world needs. A few wastewater treatment plants across the country are taking matters into their own hands and converting their plants to solar-powered energy. 

The solar farm for the Wastewater Treatment Plant in New Stanton was just finished. The Federalsburg Wastewater Treatment Plant just received over one million dollars in grant funding for the construction of a solar panel system. The city of Danbury, Connecticut is also considering a solar installation that would power their city’s wastewater treatment plant. The Diablo Water District also installed a solar power system in their facility to help them achieve their ambitious goal of being carbon neutral by 2027.

Powering water treatment plants with solar power helps the environment and it can help facilities save money because it can lock in electrical rates. It also makes facilities more resilient to power outages from natural disasters or other power grid failures. Utilities that convert their water treatment facility to solar power help their community and country work towards achieving the renewable energy goals the world is striving towards. 

Featured Video: Disinfection Byproducts in Tap Water: 5 Things To Know

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The challenge of disinfection byproduct (DBP) control in drinking water lies in balancing the varying health risks of over 600 known DBPs with the benefits of microbial waterborne illnesses prevented via disinfection. While DBPs can originate from industrial sources, they generally form in water treatment systems when natural organic matter reacts with a disinfectant, usually chlorine-based. Ongoing studies have suggested that the toxicity for any given DBP can range from having no known health effects to exhibiting links between exposure and cancer, birth defects, or reproductive disorders. Disinfectant type and dose, residual chlorine, inorganic and organic precursor concentrations, pH, temperature, and water age can impact DBP formation.

The management of DBPs in drinking water is enforced through the Stage 1 and Stage 2 Disinfection Byproduct Rule (DBPR). Collectively, the rules set maximum contaminant levels (MCLs) for total trihalomethanes (TTHM), 5 haloacetic acids (HAA5), bromate, chlorite, chlorine/chloramines, chlorine dioxide, and DBP precursors.

According to a 2019 report by the U.S. Environmental Protection Agency (EPA), the Stage 2 DBPR invoked the largest number of community water system violations between 2017 and 2018, accounting for approximately 30% of all drinking water violations. Consecutive water systems, those with surface water sources, and systems serving populations of 501 to 10,000 people experienced violations more frequently. A greater compliance challenge is experienced by consecutive systems because they have little control over the water that they receive. While treated water may have achieved compliance at the system’s interconnection, DBP concentrations can rise through the receiving distribution system.

Non-consecutive utilities experiencing compliance challenges for the Stage 1 or 2 DBPR can start by troubleshooting the system using our previous blog post on The Disinfection By-Product Challenge. Consecutive systems should coordinate with their wholesale system following the approaches suggested in the 2019 report discussed above. The preferable methods of control often lie in prevention and optimization. As your system troubleshoots the cause of high DBP concentrations, keep the community informed on your efforts as well as some basic information on the health effects and sources of DBPs. Operators can find a general overview on DBP challenges in this week’s featured video. We recommend using this video to provide customers with answers to the following questions:

  • What are disinfection byproducts?
  • How are DBPs regulated?
  • How do I know if my water has high levels of DBPs?
  • How are people exposed to DBPs?
  • How do I remove DBPs from my home’s water?

Controlling Legionella in Drinking Water Systems

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Photo Credit: CDC Public Health Image Library ID #11148 by Janice Haney 2009; Edited with cropping.

The prevalence of Legionella bacteria in drinking water and distributions systems has gained notice over the past several years due to its increasing rate of infection in the United States. Inhalation or aspiration of small aerosolized Legionella bacteria from water can cause Pontiac fever and Legionnaires’ disease most frequently in sensitive or immunocompromised populations. Between 2000 and 2015, the National Notifiable Diseases Surveillance System (NNDSS) reports that the incident rate of Legionnaires’ disease in the U.S. increased from approximately 0.42 cases per 100,000 persons to 1.89 cases per 100,000 persons. According to the Ohio Department of Health, potential reasons for this change in rate might include increased monitoring and awareness, higher population susceptibility, climate change, water-saving fixtures, and/or aging infrastructure. As of 2019 Legionnaires’ disease is reported to afflict and kill more people in the U.S. than any other waterborne disease.

Existing research indicates that, though Legionella bacteria can be found in all parts of the water treatment system, they amplify best inside protozoan hosts and near the biofilm typically found within premise plumbing or drinking water systems. The resiliency of biofilm to disinfection acts as a protective barrier for Legionella while creating an environment abundant in nutrients. Protozoan hosts also offer defense against extreme temperatures and treatment technologies. A 1994 study by Kramer and Ford found that hundreds of Legionella bacteria can be contained within a single amoeba vesicle. L. pneumophila, the species responsible for most human infections, can also differentiate into various life cycle forms that alter susceptibility to water treatment. This symbiotic relationship with other microorganisms complicates Legionella disinfection.

Hot spots for growth include showerheads, faucets, plumbing systems, cooling towers, hot tubs, fountains, and distribution systems where water stagnation, insufficient disinfectant residual, warm temperatures (77-124°F), or excess nutrients foster biofilm formation. As a result, the most frequent outbreaks from Legionella have been documented in hotels and healthcare facilities. Management of outbreaks can start at the site of these impacted buildings as well as the treatment plant. Drinking water utilities can participate in prevention by understanding the conditions that favor propagation and the methods to control growth.

The U.S. EPA established a Maximum Contaminant Level Goal (MCLG) for Legionella at zero microorganisms. While this is not an enforceable limit, the Agency believes that if Giardia and other viruses are removed or inactivated as required under the Surface Water Treatment Rule, Legionella will also be controlled. Requirements to manage bacterial contamination under the Revised Total Coliform Rule and Ground Water Rule also contribute to Legionella management. Though some systems may routinely monitor for Legionella bacteria, testing methods can often yield both false positives and false negatives. Given the complications of environmental monitoring as well as the cost, management generally starts in response to outbreaks or sporadic cases.

Ongoing research has identified that potential drinking water treatment methods for Legionella include chlorination, copper-silver ionization, ultraviolet (UV) light, ozonation, and thermal disinfection. Among these technologies, chlorine, chlorine dioxide, chloramine, and ozone are the most widely used disinfectants. A combination of these techniques offers the most effective defense against recolonization and biofilm formation. To inactivate individual bacteria as well as those contained within biofilm, operators should also pay attention to the contact time and concentration of disinfectant used during treatment. Equally important to contact time is the maintenance of disinfectant residuals throughout distribution. The National Academy of Sciences’ Management of Legionella in Water Systems details the recommendations for proper disinfection using free chlorine, chlorine dioxide, monochloramine, and technologies more commonly used by building water systems.

To effectively manage Legionella in drinking water, utilities must also collaborate with impacted buildings. Facilities that have experienced outbreaks can develop their own management plan using the Center for Disease Control’s (CDC) Developing a Water Management Program to Reduce Legionella Growth & Spread in Buildings and the World Health Organization’s Legionella and the Prevention of Legionellosis. This literature, along with the CDC training on Legionella Water Management Programs and the other resources linked within this guide will ensure that your community members, especially those at greater risk to illness, are protected from Legionella.

What Operators Should Know about PFAS in 2019

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In February of 2019, the EPA released an action plan to manage the contamination of poly- and perfluoroalkyl substances (PFASs) in water. The plan will propose an MCL regulatory determination for perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) detected under the UCMR3 by the end of 2019 and will continue environmental cleanup.

The UCMR3 found that areas with affiliated industrial sites, military fire training, and wastewater treatment plants were associated with PFOA and PFOS detection. Once released, PFASs can persist in the environment for the long periods of time, bioaccumulating in humans and animals that consume contaminated drinking water. A new health advisory for these chemicals has set the maximum recommended concentration in drinking water at 70 ppt. Exposure above this threshold may cause developmental defects, cancer, liver damage, immune issues, metabolic effects, and endocrine changes. 

Unfortunately, a health advisory is not enough to protect consumers from PFAS in drinking water as it does not legally require utilities to take action against unsafe levels. In the absence of necessary regulatory authority, several states have pushed forward with their own policies. These states have struggled with how to implement a standard without clear federal guidelines. Despite this, many states are working to set or have already set their own maximum contaminant levels. 

Options for reducing exposure to elevated PFAS contamination include changing sources, closing off contaminated wells, alteration of blending rates, or implementation of treatment. Studies have found that granular activated carbon (GAC), ion exchange, or membrane separation can treat PFAS. The removal efficiency can reach 98-99%, but it will ultimately depends on the length of the PFAS chain and the treatment method used. Installing a new treatment method is financially devastating for many systems. Alabama’s West Morgan East Lawrence Water and Sewer Authority (WMEL) estimates that the costs to install a permanent R.O. filter will reach $30-50 million. The authority has filed a lawsuit that could assist with funding the necessary upgrades.


There is currently no standardized analysis approved for PFAS testing in drinking water, however laboratories have modified the EPA groundwater detection method 537 for systems in need of monitoring. When using this method, the EPA recommends that systems “evaluate its appropriateness relative to your goals for the data.” In some locations PFAS regulators and manufacturers have also set up programs to monitor groundwater contamination. You can contact your state primacy to learn about these types of resources. 

If test results repeatedly indicate water concentrations of 70 ppt or greater for either contaminant, systems should follow any existing state regulations and promptly notify their primacy and customers. In absence of regulations, c
ustomers should be informed of the health effects and advised to consume bottled water until a better option is available. Download a consumer-friendly fact sheet from CDC.

An Overview of Drinking Water Fluoridation

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Despite a long history of dental health benefits, the fluoridation of community drinking water remains a topic of concern for many customers. Given this apprehension, water operators must be able to explain the societal impacts and history of water fluoridation to alleviate concerns. 

Fluoridating drinking water first began in 1945 in Grand Rapids, Michigan. The new practice resulted in a clear reduction in cavities and tooth decay, one of the most prevalent chronic diseases experienced during childhood to this day. As of 2014 about 74% of consumers under a community public water system received fluoridated water. According to the Center for Disease Control (CDC), school children in communities without fluoridation have 25% more tooth decay compared to children in treated communities. These cavities can cause a variety of issues related to pain, diet, sleep, physical health, and mental health.

With cost efficiency community fluoridation overcomes disparities in oral health regardless of community size, age, education, or income level. A dental health study found that the savings from fluoridation in communities of 1,000 people or more exceeded program costs by $20 per every dollar invested. When Juneau, Alaska voted to end fluoridation in 2007, a study found that children six years and under had an increase of one dental cavity per year, roughly equivalent to $300 in dental costs per child annually. Juneau’s increase in cavities was also reflected in adults.

All water contains some levels of naturally-occurring fluoride though these levels are often too low for health benefits. In untreated water, fluoride levels vary considerably with geology and land practices. Fluoride is introduced to water when dissolved from the Earth’s crust into groundwater or discharged from fertilizer and aluminum factories. Systems with fluoridation should set final levels near 0.7 mg/L as suggested by the Department of Public Health. This concentration factors for other sources of consumer fluoride exposure such as toothpaste. Fluorosilicic acid (FSA) is most commonly used in water treatment. Though fluoridation decisions are left to a state or local municipality, the EPA has established federal standards for the upper limits allowed in drinking water.

At high levels fluoride can cause the development of bone disease and tooth mottling. As a result, the EPA has set both the Maximum Contaminant Level Goal (MCLG) and the MCL for fluoride at 4 mg/L. Levels higher than 4 mg/L can lead to increased rates of bone fracture, Enamel Fluorosis, and Skeletal Fluorosis. If systems find fluoride concentrations higher than the MCL, they are required to notify customers within 30 days and potentially install treatment methods such as distillation or reverse osmosis to remove the excess fluoride. 

The EPA has also set a secondary standard for fluoride at 2.0 mg/L. The secondary standard is intended to be used as a guideline for an upper bound level in areas with high levels of naturally occurring fluoride. Below this level, the chance for tooth mottling and more severe health impacts are close to zero. Even if the secondary standard is reached, systems must notify customers. In the U.S. very few systems have exceeded the fluoride MCL at all. Where violations have occurred, the concentrations are generally a result of natural, geological conditions. 

Even with this track record, some concerned customers are still weary of fluoridation. When customers broach fluoridation concerns, operators can offer educational materials and refer customers to consumer confidence reports. The CDC and the EPA offers a variety of consumer-friendly educational material that operators can reference in addition to the resources linked in this blog post. Remember that good customer service starts by establishing a trusted relationship with your community.

What's on the Drinking Water Radar for the Year Ahead: 2019

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Being a small-town water operator is not easy; it is up to you to ensure the quality of your community's water day-in and day-out, often with very limited resources. Let WaterOperator.org help you meet the challenge head-on with this list of tools and resources to put on your radar for the year ahead:

  • Have you gotten in the groove yet with the new RTCR requirements? Here are two new documents from the USEPA designed to help small public water systems: Revised Total Coliform Rule Placards and a Revised Total Coliform Rule Sample Siting Plan with Template Manual. Additional compliance help, including public notification templates, a RTCR rule guide, a corrective actions guidance and more can be found here.
  • While we know your hands are full just getting the job done, there are new and emerging issues you may have to deal with in the year ahead. For example, this past year many communities have been dealing with PFAS contamination issues. This ITRC website provides PFAS fact sheets that are regularly being updated on PFAS regulations, guidance, advisories and remediation methods. Especially of interest is this excel file that has begun to list the different state standards and guidance values for PFAS in drinking water as they are developed. Be sure to check back often for updates.
  • Your utility may also have to adjust to new compliance rules in the coming year. In Michigan, for example, a new Lead and Copper Rule arising from the water crisis in Flint has gone into effect, making it the strictest in the nation. Other states, such as Ohio, have also adopted tougher standards, or are now requiring schools to test for lead. Oregon has established temporary rules that will require drinking water systems in the state using certain surface water sources to routinely test for cyanotoxins and notify the public about the test results.
  • With a warming climate, these incidences of harmful algal blooms in surface water are on the increase, causing all sorts of challenges for water systems that now have to treat this contaminant. This cyanotoxin management template from the EPA can help assist you with a plan specific to your location.
  • Worker turnover and retirements will still be an issue in 2019. According to this article, the median age for water workers in general (42.8 years) and water treatment operators specifically (46.4 years) are both above the national average across all occupations (42.2 years). You can keep transitions as smooth as possible by using EPA's Knowledge Retention Tool Spreadsheet and/or this Electronic Preventive Maintenance Log.
  • New Tech Solutions: A UMass lab focusing on affordable water treatment technologies for small systems will be rolling out its Mobile Water Innovation Laboratory in 2019 for on-site testing. In addition, the facility is testing approaches to help communities address water-quality issues in affordable ways. "Early next year, in the maiden voyage of the mobile water treatment lab, UMass engineer David Reckhow plans to test ferrate, an ion of iron, as a replacement for several water treatments steps in the small town of Gloucester, MA.

But even without all these challenges and new ideas for the future, simply achieving compliance on a day-to-day basis can be tricky - if this sounds familiar, you may want to check out our recent video on how operators can approach the most common drinking water compliance issues.