Radium concentrations in drinking water are drawn from EWG’s Tap Water database, and represent the average of all samples of treated drinking water collected from 2010 to 2015 for each water system. Samples reported as non-detections are entered as zero, which could underestimate the actual radium concentration in drinking water.
Federal drinking water regulations set a Maximum Contaminant Level, an enforceable legal standard, of 5 picocuries per liter (pCi/L) for the combined level of two isotopes of radium: radium-226 and radium-228. Some water utilities and states report individual levels of these isotopes, while others report a single combined radium value of a specific sample. When the combined level was not reported by the water utility, EWG added measurements of radium-226 and radium–228 to calculate it, as available.
This map displays radium data for 1,850 community water systems serving more than 10,000 customers, and 1,620 community water systems serving between 3,301 and 10,000 customers. The water system locations were mapped based on the Environmental Protection Agency’s Safe Drinking Water Information System, or SDWIS. Locations are approximate and are meant to visualize the general area served by a specific water system – not to give the specific address of the water treatment plant. The map does not include water systems that did not detect radium between 2010 and 2015. It also does not include those water systems for which EWG could not confirm geographic locations.
On the map, dots indicating water system locations are color-coded according to the combined radium levels. Dot size reflects the water system’s size of above or below 100,000 customers. Any changes in water sources and treatment, and water quality after 2015, are not reflected in EWG’s analysis. For more detail on data reporting methods for EWG’s Tap Water Database, read our Methodology.