* Because MTBE is an unregulated contaminant, utilities may not be required to report all detections to the state.

Important Note: A reported detection of MTBE does not mean the contaminant was found at any level in finished drinking water that the water system delivered to consumers. Some results reflect tests conducted on a water source, others may reflect results from finished tap water. MTBE contamination as low as 2 parts per billion produces a harsh chemical odor that renders the tap water undrinkable. For that reason, in the vast majority of the affected communities water utilities have taken steps to protect consumers, often with costly remedial action, as soon as MTBE is detected and before water is delivered. Water utilities either blend contaminated water with clean sources to dilute the MTBE in finished water, install costly systems to remove the chemical, or abandon tainted wells and shift to clean sources. Community water suppliers would be unable to recover the cost of these remedies from MTBE manufacturers under the liability shield Republican leaders have proposed to include in pending national energy legislation.

Data are primarily for community water systems. Comparable data are not available for MTBE contamination of the majority of private wells.