From Energy News
UCB Rain Water Sampling Results, University of California, Berkeley, Department of Nuclear Engineering:
Iodine-131 level in rainwater sample taken on the roof of Etcheverry Hall on UC Berkeley campus, March 23, 2011 from 9:06-18:00 PDT
20.1 Becquerel per liter (Bq/L) = 543 Picocuries per liter (pCi/L) — Conversion calculator here.
The federal drinking water standard for Iodine-131 is 3 pCi/L. (Press Release)
Agency for Toxic Substances and Disease Registry for Iodine, CDC, April 2004:
EPA has set an average annual drinking water limit of 3 pCi/L for Iodine-131 so the public radiation dose will not exceed 4 millirem