A report by the USGS on radium concentration in drinking water aquifers nationwide shows that the water wells tested in Arizona are all below 1 picocurie per liter. However, only a handful of wells in Arizona were tested, all in alluvial aquifers in the south.
No tests are reported from the Colorado Plateau, which has some of the highest concentrations and largest deposits of uranium in the nation. EPA notes that "Radium is a naturally occurring silvery-white radioactive metal formed when uranium decays in the environment."
The USGS report states "Radium is a naturally occurring radioactive element and known carcinogen that usually is present at low levels in rocks, soils, and groundwater. Its presence in groundwater is largely the result of minerals dissolving from weathered rocks and soils. The US Environmental Protection Agency (USEPA) has established maximum contaminant level (MCL) for combined Ra-226 plus Ra-228 of 5 picocuries per liter (pCi/L) for public water supplies."