Environmental Health News

Keeping Seattle's Drinking Water Safe

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Clean drinking water is cheap and easy to access, but water everywhere may be vulnerable.

Clean drinking water is cheap and easy to access, but water everywhere may be vulnerable. 



National Safe Drinking Water Week, May 4–10, celebrated a valuable resource. Turn on the kitchen tap in any home in Seattle and out comes water meant to quench our thirst, rinse our fruits and vegetables, and clean our dishes. We don't think twice about these activities as clean water is cheap and easy to access in our city.

Yet, water everywhere may be vulnerable. We were reminded of this in January, when a chemical spill deprived 300,000 residents in Charleston, West Virginia, of tap water. An unregulated chemical leaked from a storage tank into the river and overwhelmed the city's treatment facility.

The Safe Drinking Water Act gives the US Environmental Protection Agency (EPA) authority to set drinking water standards and requires states to develop and implement source water assessment and protection programs. In fact, there are a slew of different agencies, organizations, and industries involved in ensuring potable water. The public's understanding of risks to a safe supply of water and practicing good stewardship is critical.

In our department, researchers are developing tools to assess risks at the tap, measuring water treatment byproducts that may pose risks to health, and providing training to water system managers and operators to better protect water sources.

Ilustration of Seattle's Drinking Water Treatment and Delivery Process.Drinking water is protected at multiple points, from source to tap. First, preventing contamination in the watershed is key (1). Then at a water treatment facility, source water is processed and disinfected to achieve optimal quality before being piped to customers (2). If a main breaks, water pressure is maintained by diverting water (3). That’s how a utility ensures that the water in your tap is clean and safe to drink (4). Illustration: Letty Limbach.

At the Tap: Assessing Public Health Risk

Under Seattle lies an impressive web of plumbing. More than 1,600 miles of drinking water mains supply about 140 million gallons of water per day to approximately 1.4 million people in the greater Seattle area.

Similar to other places in the country, Seattle has pipes that are commonly more than a century old. The older the pipes, the more likely they will fail, and many of them do. Nationwide, the EPA estimates there are 240,000 main breaks every year. Replacing all the pipes would be a mammoth task. The American Water Works Association calculates the price tag could reach $1 trillion in 25 years.

An aging infrastructure means increased risks to public health. If a break occurs, water pressure in the distribution network can drop, and slurry around the pipe may be pulled into the water flow. That muddy water can contain harmful pathogens, such as Cryptosporidium, Giardia, and Norovirus. Not surprisingly, the American Society of Civil Engineers gave our nation's drinking water infrastructure a D on its report card last year.

State and federal laws require suppliers to notify customers if their drinking water may not be safe to drink. In Seattle, only three boil-water advisories have been issued since 2008, said Nicole Van Abel, a PhD candidate in our Environmental and Occupational Hygiene program who has been studying water system infrastructure. "The advisories," explained Wylie Harper, drinking water quality manager at Seattle Public Utilities (SPU), "were precautionary due to loss of pressure." There was no evidence of contamination.

When emergencies happen, suppliers have to act fast. On October 8, 2013, when a water main broke and hundreds of thousands of gallons of water flooded University Village, valves were quickly shut off to maintain pressure. Within minutes, Van Abel said, engineers were dispatched to analyze risks to residents, and Harper pointed out no advisory was warranted.

The computational model Van Abel is building for her dissertation may help municipalities manage water systems by being able to anticipate public health risks if their system is compromised. She spent six months at KWR Watercycle Research Institute in the Netherlands where she developed a portion of the model. Van Abel's model estimates the public health risk in a water distribution system by calculating water pressure, contamination levels and locations, and frequency of water usage in the home. Her model combines this information with an index of microorganisms in the environment and their potential to cause illness. The computation builds "what-if " scenarios to determine areas in the distribution system that may need attention. Municipalities could use the information to determine how to allocate funds.

Water Treatment and Toxicity

Pipes from the Tolt Water Treatment FacilitySource water is filtered at the Tolt Water Treatment Facility. Photo: Ian Edelstein, Seattle Municipal Archives 111862.

A century ago, before chlorination and filtration became common water treatment practices, the US saw frequent outbreaks of cholera and typhoid.

Chlorine is still the most commonly applied disinfectant for municipal drinking water. Others include ozone, chlorine dioxide, chloramine, and ultraviolet radiation. Disinfection is typically done in two steps. The primary disinfectant inactivates microorganisms and breaks up inorganic material, and the secondary disinfectant is added to maintain a residual disinfectant in the water supply to wipe out any lingering pathogens.

In Seattle, there are two water treatment facilities: Cedar and Tolt. In both, ozonation inactivates any Giardia and Cryptosporidium present. In the Cedar facility, UV light is also applied, while filtration is done at the Tolt plant. Then in both facilities, free chlorine is applied to maintain a residual disinfectant in the distribution system.

Yet, treating water may bring other kinds of concern. Researchers in our department as well as nationally are trying to understand the risks of disinfection byproducts. Disinfection byproducts are chemicals formed by the reaction of disinfectants with organic and inorganic materials in source water.

While the amount present can be miniscule, the toxicity of byproducts like trihalomethanes and haloacetic acids can be significant. Hundreds of byproducts from different water treatment processes have been identified. EPA regulates 11 byproducts that have been associated with cancer, reproductive, and developmental health risks. In Seattle, these disinfection byproducts are well below regulatory limits.

To meet EPA's 2006 standards for certain byproducts, some treatment facilities around the country have switched to chloramination as their secondary disinfection, a process of using ammonia as well as chlorine. Seattle does not use chloramination.

The EPA's Integrated Disinfection Byproducts Mixtures Research Project (the 4Lab Study) is developing chemical and toxicological assessments using two treatment protocols: chlorination and chloramination, looking at the formation of byproducts and their mixtures.

A number of effects from chloraminated byproducts have been documented, even though they remain largely unregulated, explained environmental chemist Gretchen Onstad, acting assistant professor in our department. She studied under one of the lead investigators in the 4Lab Study and wrote her doctoral dissertation on halogenated furanones in drinking water. These mutagenic disinfection byproducts are potential human carcinogens and yet are unregulated.

Onstad recently received a $175,000 grant from the EPA to identify and test levels of 35 different byproducts and compounds in drinking water for the 4Lab Study.

The findings, explained Onstad, "will tell us more about the toxicity of treated drinking water. Part of the puzzle in cases of cancer or reproductive or developmental effects associated with drinking chlorinated or chloraminated water is that we can't account for those effects based on byproducts we've identified. Is cancer coming from byproducts we haven't identified or from the chemical mixtures' effect?"

Or could it be something else? The researchers hope to answer these questions.

Watershed Protection: Sharing the Burden

Masonry Pool.Masonry Pool is part of the Cedar River watershed. Along with the Tolt River, these watersheds provide drinking water to Seattle area residents. Photo: Courtesy Seattle Municipal Archives 103739.

Most of Seattle's water comes from the Cedar River, and everything north of 85th Street comes from the South Fork Tolt River.

"Seattle has highly protected watersheds because of the efforts of people over the last 100 years to secure a water supply away from development and to prioritize the protection of that land. Few cities in the country have such protected watersheds," explained Jim Nilson, a water quality engineer at SPU.

Thousands of public water systems serve Washington state's population. About 200 of these supply drinking water to the majority of residents and rely on surface water, such as rivers and streams. Surface water sources are inherently more vulnerable to contamination and loss of supply.

"When the watersheds are protected, treatment costs and the probability of water system emergencies are lower," explained Kitty Weisman, Source Water Protection Program manager at the Washington State Department of Health's Office of Drinking Water.

Small and medium-sized communities may have limited financial or staff resources, Weisman explained. Two-thirds of the drinking water utilities that rely on surface water don't own the land surrounding the watershed.

Map of drinking water sources near federal and state lands around Seattle.Drinking-water sources near federal and state lands near Seattle are depicted in this slice of a statewide map. Credit: Washington State Department of Health, Office of Drinking Water. (Click image to enlarge. Download a PDF of the full WA state map.)

The Safe Drinking Water Act gives state and federal agencies regulatory authority over drinking water operations and distribution. But when it comes to source water, activities on private land fall under local land-use regulations, which may not protect drinking water. Yet, these activities, from farming and forest practices to building and development, can directly influence the quality of water.

Some watersheds are particularly fragile due to steep slopes and unstable soils, explained Weisman. Forest practices and development may lead to erosion and increase turbidity, particularly after heavy winter storms. Downstream, a treatment plant may be forced to shut down because it is only designed to treat water within a certain turbidity range. The community would then need to spend time and money to find an alternate drinking water source.

Jonathan Nagata, a concurrent master's student in Environmental Health and the Evans School of Public Affairs, is working with Weisman and the Office of Drinking Water to develop and lead a training series for water treatment operators and managers. The series, which begins later this year, will cover forest practice regulations and how to collaborate with watershed landowners.

"It's like worlds colliding," Nagata said, "Public Health meets policy meets water quality meets watershed management—a culmination of everything in my educational career." His analogy can also refer to all the different people, agencies, and operations that protect a single resource: the water we drink from the tap.

In Seattle, we're particularly fortunate. As Harper said: "Seattle's water quality is exceptionally good, from source to tap, due to our pristine watersheds and state-of-the-art treatment facilities."

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