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Community Water


What is a Community Water System?

In Oregon, more than 85% percent of the population obtains their drinking water from community water systems (CWS). As defined by the Environmental Protection Agency (EPA), a community water system (CWS) supplies water to the same population year-round. It serves at least 25 people at their primary residences or at least 15 primary places of residence (for example, municipalities, mobile home park, sub-divisions). These systems are subject to treatment and monitoring regulations set by the EPA under the Safe Drinking Water Act. State agencies and water suppliers work together to help ensure that drinking water contamination levels are as low as possible by protecting water sources, treating water to remove contaminants and monitoring water quality to identify and resolve problems quickly.

Congress established the Safe Drinking Water Act in 1974, which allows the EPA to set enforceable maximum contaminant levels (MCL) for specified contaminants based on the best available scientific evidence. Drinking water standards are usually set at a fraction of the no observed adverse effect levels because potential health risks are often unknown or hard to predict. EPHT is tracking CWS water testing results for 10 regulated contaminants with the largest potential public health impacts.

Types of contaminants we track and impact on health:

Arsenic is an element that is widely distributed in the environment and forms a number of water-soluble compounds. High concentrations occur naturally in certain geologic formations and artificially as a result of some industrial and agricultural activities. Food is the primary source of arsenic intake for most people, although it can also be absorbed by breathing polluted air or drinking contaminated water. In areas where groundwater arsenic levels are high, drinking water can be the primary source of exposure. At very high doses, arsenic causes immediate effects including nausea, vomiting, diarrhea and death. Long term exposure to arsenic at lower levels can cause cancer and other health effects, including skin lesions, cardiovascular disease, neurological problems and developmental and reproductive issues. The EPA has set a MCL of 10 micrograms per liter (µg/L) for arsenic. In Oregon, some community water systems regularly have arsenic levels above the MCL; very high levels are sporadically detected around the state.

Disinfection byproducts (DBP) are formed when chlorine reacts with minerals and organic material during treatment of drinking water for pathogens. Due to its effectiveness, nearly all systems use chlorine to disinfect water. Haloacetic acids (HAA5) and trihalomethanes (THM) are the primary types of byproducts produced, although not necessarily the most toxic. The types and concentrations of byproducts depend on the source of the water and amount of chlorine used. Drinking contaminated water is the principal route of exposure to HAA5. The major exposure route for THM is inhalation during showering, bathing, general cleaning and washing clothing and dishes. Over long periods of time, exposure to elevated levels of DBPs can damage the central nervous system, liver, kidneys, eyes and reproductive systems and may increase the risk of birth defects and cancer. The MCLs for HAA5 and total THM (TTHM) are 60 µg/L and 80 µg/L, respectively. In Oregon, HAA5 and TTHM levels exceeding the MCLs are common, occurring primarily in smaller systems with less control of disinfectant concentrations.

Nitrate is the most common contaminant in ground water aquifers worldwide. It occurs in water contaminated by fertilizers, sewage, septic tanks and decaying organic material, such as animal waste. As a result of human activities and population growth, nitrate is increasing in surface water and aquifers. The primary route of exposure is drinking contaminated water. High nitrate levels can cause methemoglobimia or "blue baby syndrome" in infants who receive formula mixed with contaminated water. In adults, individuals who don’t produce enough methemoglobin reductase or have low stomach acid are susceptible to the effects of nitrate. A wide variety of medical conditions, including food allergies, asthma, hepatitis and gallstones may be linked to nitrate. The EPA has set a MCL of 10 milligrams per liter (mg/L) for nitrate in drinking water. In Oregon, nitrate levels exceeding the MCL are common and occur primarily in agricultural areas.

About the measures:

The community water system (CWS) contaminants tracked by EPHT are arsenic, di (2-ethylhexyl) phthalate (DEHP), haloacetic acids (HAA5), and nitrate. The measures for each contaminant are the number of people served and number of community water systems by the mean and maximum concentrations detected. A secondary table lists individual water systems with mean and maximum detections that exceed the maximum contaminant level (MCL) set by the Environmental Protection Agency (EPA).

The presence of contaminants in drinking water cannot be assumed to reflect exposure because overall water consumption and the proportion of water consumed that comes from the tap is variable. Individual differences in water use behaviors further complicate efforts to estimate exposure from drinking water measurements. Assessment is further hampered by the fact that many water systems obtain their water from more than one source, so the actual contaminant level at a particular tap may be the result of mixing water from different sources.

About the data:

Drinking water contaminant concentrations are based on samples taken from community water systems (CWS). Data from emergency sources are not included. Water systems test on various schedules depending on the contaminant, water source, size of the systems and previous testing results, which can create gaps in the data and may not adequately capture temporal variation, particularly for low levels.

Water system name, ID number, primary county served and population served are provided for each water system in exceedance of the standards. Due to the design of the source database, estimates of the population served for each water system are from the year that the Oregon Drinking Water Program database was queried by EPHT. This may result in an overestimation or underestimation, depending on whether the population has increased or decreased over time. Population estimates displayed for years from 2000 to 2011 are 2011 estimates; estimates for each year after 2011 are for that year.

Only water systems for which samples were available are shown in these measures. Values are not imputed for time periods in which samples were not taken. Systems sample quarterly if the running annual average exceeds the standard. The change in sampling frequency may affect the ability to make meaningful comparisons over time. Since contaminant levels in water can vary substantially over time, high levels may not be captured even by quarterly sampling.

Related Indicators:

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