http://water.epa.gov/drink/contaminants/index.cfm#Radionuclides This does not mention I-131 but has standards for activity in general.Been to that one. I-131 is a beta emitter, so it would be covered under "gross beta" where the limit is 4 mrem/year. Notice, this is not given in pCi or Bq, and the dose rate depends on the specific isotope involved. So where does the 3 pCu/L come from?
Is that Klingon in your tagline?