State and local officials will make decisions about continued use of tap water based upon the conditions on-site during a radiological emergency. The drinking water PAG provides information they will consider, including two scientifically-based levels to be avoided (1 mSv (100 mrem) for infants, children aged 15 and under, pregnant women and nursing women; 5 mSv (500 mrem) for anyone over age 15 excluding pregnant women and nursing women) for periods up to one year.
Since this is only guidance, the levels selected by your state or local officials will depend on the type and severity of the incident. You may not be instructed to stop drinking tap water. Your water department—in coordination with state/local officials and emergency managers—may choose to either use water from storage tanks that have not been impacted by radiation, purchase water from a neighboring town, transport water in tanker trucks or provide bottled water to the community.