Water Research Foundation Resources State of the Science

​Summaries and primers from our most current research on topics important to the water community.

1,2,3-trichloropropane (TCP)
1,2,3-trichloropropane (TCP) is a manmade pesticide impurity and solvent/degreaser suspected to cause cancer in humans. No federal maximum contaminant level (MCL) has been set for TCP in drinking water. However, various states have established health-based drinking water guidance values. TCP has been detected in hundreds of surface water and drinking water sources at levels of 0.1–100 μg/L. Conventional water treatment practices have proven to be relatively ineffective at removing TCP from water. Despite its high Henry’s constant, air stripping is not cost effective for achieving the eventual public health goal. Ultraviolet light (UV), along with hydrogen peroxide, has shown some degradation of TCP, although the degradation rate constant was fairly low. Currently, granular activated carbon (GAC) is the only viable treatment option for TCP removal.

 
1,4-dioxane is a synthetic industrial chemical that is completely miscible in water. The largest sources of 1,4-dioxane in drinking water sources are wastewater discharge, unintended spills, leaks, and historical disposal practices of its host solvent, 1,1,1-trichloroethane (TCA). 1,4-dioxane readily dissolves into groundwater, and its movement is not retarded significantly by sorption to soil particles. It is highly mobile, recalcitrant to microbial degradation, and has a low tendency to volatilize from water. Conventional water treatment practices (e.g., coagulation, sedimentation, and filtration), aeration, GAC adsorption, ozone, UV, and biofiltration have proven to be ineffective at removing 1,4-dioxane from water. Advanced oxidation processes including a combination of hydrogen peroxide and ferrous iron, ozone and hydrogen peroxide, and UV and hydrogen peroxide have been shown to be effective for oxidizing 1,4-dioxane.
 
Chloramines are a class of oxidants formed by the reaction of chlorine and ammonia. In drinking water treatment, chloramines are primarily used as a secondary disinfectant to provide a residual in the distribution system. Chloramination has been used in drinking water treatment since the early 1900s, but its use has been low compared to that of chlorine. In recent years, a large number of utilities have switched from chlorine to chloramine as a secondary disinfectant, primarily to comply with the U.S. Environmental Protection Agency’s (EPA) Stage 1 and Stage 2 Disinfectants and Disinfection By-Products Rules (D/DBPR). Chloramination can be a complex process and improper management can lead to unintended consequences including nitrification, formation of non-regulated DBPs, and deleterious effects on some elastomeric materials used in the distribution system. Since chloramine use has been increasing, water professionals need to understand the various aspects of chloramination with the goal to better manage and operate their systems and minimize unintended consequences.

The provision of a safe and sustainable drinking water supply is one of the hallmarks of a successful society. Treated drinking water entering distribution systems in virtually all U.S. public drinking water systems meets regulations and is microbiologically safe. However, the opportunity for microbial contamination from decades to century old water distribution systems is increasing with time. Thus, increased health risk to consumers should be a driving factor in accelerating reinvestment in America’s aging water distribution water systems.
 
Cyanobacteria are photosynthetic bacteria that are common in all freshwater and marine environments. They were historically called blue-green algae but their structure, genetics, and physiology clearly identify them as bacteria. Cyanobacteria in freshwater systems are widely recognized as sources of toxins (cyanotoxins) and unpleasant tastes and odors in water supplies. Cyanobacteria are a normal component of the natural biota and tolerate a wide range of climatic conditions and environments. A rise in the number of cyanobacterial blooms, caused by eutrophication from decaying plant materials and man-made pollution, is resulting in the production of more taste and odor compounds and natural toxins, which demands the attention of water treatment authorities. Although cyanotoxins are less commonly found in drinking water than taste and odor compounds, their high toxicity is of great concern. Due to global climate change, toxin-producing cyanobacteria are spreading into more temperate regions and becoming a more widespread problem.
 
Fluoride is a naturally occurring compound derived from fluorine, the 13th most abundant element on Earth. It is found in rocks, soil, and fresh and ocean water. Fluoride is present naturally in almost all foods and beverages including water, but levels can vary widely. It is added to drinking water to provide public protection from dental caries. The current U.S. Public Health Service recommendation for the optimal level of fluoride in drinking water is 0.7 mg/L. In 2015, WRF produced this document to summarize the occurrence of fluoride in natural waters, regulations, and treatment. It also contains six case studies, summarizing community water fluoridation efforts in six U.S. cites.
 
Hexavalent chromium or Chromium (VI), is a form of the metallic element chromium. It is generally used or produced in industrial processes and has been demonstrated to be a human carcinogen when inhaled. Water sources can be affected by hexavalent chromium naturally or through contamination plumes from industrial centers, landfills, and improper discharge of industrial processing streams. The health effects of hexavalent chromium through ingestion—the dominant exposure route for drinking water—have seen limited study and yielded uncertain conclusions.
 
​The water sector and the planning and development community have a symbiotic relationship which usually goes unrecognized, and therefore, is not realized. Without adequate water resources and water infrastructure, urban development and redevelopment can be stymied. An approach gaining favor with water managers is Integrated Urban Water Management (IUWM), sometimes also called One Water. IUWM principles recognize that water from all sources must be managed holistically and cooperatively to meet social, economic, and environmental needs. This state of the science, written by WRF staff and originally published by the American Planning Association in their online publication, PAS Memo, explores the challenges and opportunities of IUWM and presents the need for cooperation and leadership among urban planners and water service personnel using IUWM to move toward more water-resilient and sustainable communities.
 
This summary of relevant completed and ongoing Water Research Foundation (WRF) research projects is meant to help with a basic understanding of the issues surrounding lead and copper. Since the late 1980’s, WRF has funded over 45 research projects related to lead and copper corrosion with a combine value at more than $14 million. All projects with Pb and Cu corrosion implications are described in this paper, which is updated annually.

Manganese is an element that occurs naturally in water, soil, air, and food, and can be found in North American ground and surface water supplies. Manganese chemistry, treatment, and impacts can be very complex. Typically, utilities have problems with manganese when they experience concentrations spikes and are not prepared to treat it. Conversely, utilities that have consistently higher levels of manganese usually have an effective treatment plan. Water utilities have historically managed manganese because of its potential to cause aesthetic issues such as black water events, unpleasant tastes and odors, and laundry staining, as well as its tendency to accumulate in distribution systems and cause operational problems.

Microplastics (MPs) are plastic particles under 5 mm in size (but seldom sampled <0.3 mm). They enter the environment through human use. Some plastics are manufactured as MPs; however, larger plastic debris can degrade into micro-sized particles over time with exposure to sun and water. Microfibers, one category of microplastics, have been found in fish and marine animals. However, more research is needed on the toxicology of MPs, including microfibers, and the overall relevance for fresh­water resources, drinking water, and human health.
 
Perchlorate is a chemical primarily used in the manufacturing of explosives and rocket propellants for the defense and aerospace industries. Low levels of ammonium perchlorate have also been found to occur naturally in the environment. In 1997, elevated levels of perchlorate were discovered in California drinking water supplies using a new, more sensitive detection technique. More recent occurrence studies have found perchlorate contamination in both groundwater and surface waters serving as drinking water sources for more than 16 million people in at least 26 states nationwide, though most often in the Southwest.
 
Per- and polyfluoroalkyl substances (PFASs), also commonly referred to as perfluorinated chemicals or PFCs, are a group of manmade chemicals with past and current uses in industrial processes and consumer products. PFASs are used in firefighting foams, coating for food packaging, ScotchGardTM, and TeflonTM, among other products. Exposure to PFASs can occur through use of products or consumption of food or water containing PFASs. These substances do not break down easily and therefore persist in the environment. They are also soluble in water and can enter source waters through industrial releases, discharges from wastewater treatment plants, stormwater runoff, release of firefighting foams, and land application of contaminated biosolids. There are not currently any federal regulations limiting PFASs in water, but the EPA is considering whether to establish Maximum Contaminant Levels for PFASs in drinking water. Conventional treatment does not effectively remove them from water. Activated carbon and anion exchange can remove many PFASs, but the most effective treatment technologies are nanofiltration and reverse osmosis.
 
Radionuclides are radioactive isotopes that can occur naturally or result from manmade sources. Natural radiation comes from cosmic rays, naturally-occurring radioactive elements in the earth’s crust, and radioactive decay products. Since these radionuclides are present in soil and rock, they can also be found in groundwater and surface water. Typical radionuclides found in drinking water sources are isotopes of radium, uranium, and radon, among others. Fission products from manmade nuclear reactions are also of concern today, particularly radioactive cesium and iodine. The three basic types of radiation are alpha particles, beta particles, and gamma rays. Alpha particles are positively charged helium atoms; beta particles are negatively charged electrons, and gamma rays are high-energy electromagnetic waves.
 
In addition to making sure the water at customers' taps is safe to drink, water providers must also meet customer expectations for the water's aesthetic characteristics—its taste, odor, and appearance. Although most contaminants that cause aesthetic problems in drinking water are not considered a threat to human health, unpleasant tastes and odors are the most common cause of customer complaints, and they often play a role when customers choose alternative supplies such as bottled water. Because aesthetic characteristics are not usually related to public health, they are regulated by secondary standards—water quality goals that are not mandatory or enforced in most states. Nevertheless, customers who find the taste or smell of tap water disagreeable often assume the water is of poor quality and, therefore, unsafe to drink. Thus, water utilities need to be proactive in identifying and mitigating taste and odor episodes.