Key to abbreviations:

• AL-Action Level: The concentration of a contaminant which, if exceeded, triggers treatment or other requirements that a water system must follow.
• MCL-Maximum Contaminant Level: The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to the MCLGs, as feasible, using the best available treatment technology.
• MCLG-Maximum Contaminant Level Goal: The level of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs allow for a margin of safety.
• MRDL-Maximum Residual Disinfectant Level.
• MRDLG-Maximum Residual Disinfectant Level Goal.
• N/A-Not Applicable (does not apply).
• nd-No Detection.
• 90th Percentile Level-This is the value obtained after disregarding 10 percent of the samples taken that had the highest levels. For example, in a situation in which ten samples were taken, the 90th percentile level is determined by disregarding the highest result, which represents ten percent of the samples. Note: In situations when only five samples are taken, the average of the two with the highest levels is taken to determine the 90th percentile level.
• NTU-Nephelometric Turbidity Unit: Used to measure clarity in drinking water.
• oocysts/L-Oocysts/Liter: A measurement of the number of Cryptosporidium (or Giardia) spores.
• ppb-Parts per billion, which can also be expressed as micrograms per liter (μg/l).
• ppm-Parts per million, which can also be expressed as milligrams per liter (mg/l).
• TT-Treatment Technique: A required process intended to reduce the level of a contaminant in drinking water.

A Closer Look at Contaminants:

The sources of drinking water (both tap water and bottled water) include rivers, lakes, streams, ponds, reservoirs, springs, and wells. As water travels over the surface of the land or through the ground, it dissolves naturally-occurring minerals and, in some cases, radioactive material, and can pick up substances resulting from the presence of animals or from human activity.

Contaminants that may be present in source water include:

• Microbial Contaminants: Such as viruses and bacteria, which may come from sewage treatment plants, septic systems, agricultural livestock operations, and wildlife.
• Inorganic Contaminants: Such as salts and metals, which can be naturally-occurring or the result from urban stormwater runoff, industrial or domestic wastewater discharges, oil and gas production, mining, or farming.
• Pesticides and Herbicides: Which may come from a variety of sources such as agriculture, urban stormwater runoff, and residential uses.
• Organic Chemical Contaminants: Including synthetic and volatile organic chemicals, which are by-products of industrial processes and petroleum production, and can also come from gas stations, urban stormwater runoff, and septic systems.
• Radioactive Contaminants: Which can be naturally-occurring or be the result of oil and gas production and mining activities.