Exposure to contaminants in drinking water can occur from drinking contaminated water, eating food that has been washed with contaminated water, inhaling steam from running hot water (in the sink or shower), or absorbing water through skin contact (in the shower or swimming pool). Potential immediate or long-term health problems caused by drinking water contaminants vary based on the type of contaminant, how the contaminant enters the body, the amount of the contaminant that enters the body, and how often or for how long the exposure occurs. Health impacts from different contaminants may include gastrointestinal illness, reproductive problems, cancer, and developmental and neurological disorders.
Most health effects are caused by long-term exposure to contaminants that exceed the maximum contaminant level (MCL) in drinking water. Some contaminants may cause acute health effects among certain groups following short-term exposure. For example, infants exposed to nitrate above the MCL of 10 mg/L in drinking water could become seriously ill within a few days and may die if untreated.
According to the Centers for Disease Control and Prevention (CDC), 42 drinking water-associated disease outbreaks were reported in the United States in 2013-2014, accounting for at least 1,006 cases of illness, 124 hospitalizations, and 13 deaths. California has not had any known drinking water-related disease outbreaks in the last 9 years. However, these statistics are based on outbreaks (sudden increases in cases of disease above what is normally expected for a given time period and population) and do not indicate that no one in California has experienced adverse health impacts from drinking water contaminants.
Acute health outcomes such as diarrhea may be easier to link to contaminated drinking water than long-term health outcomes and, as a result, may be reported more frequently as water-related illnesses. For example, consuming contaminants like bacteria or viruses may cause gastrointestinal illness resulting in diarrhea or vomiting within a few days or hours of drinking contaminated water. Alternatively, contaminants like lead, arsenic, nitrate, or disinfection byproducts may be consumed in small quantities for many years before any noticeable health impacts occur. These long-term health impacts, such as reproductive problems, cancer, and developmental and neurological disorders, are also caused by other exposures and genetic factors. For these reasons, long-term health impacts are more difficult to link to drinking contaminated water.