absorption of I-131 in water vs milk

I've been watching this thread and others on I-131 and other radioisotopes in rain water, as well as smaller amounts in drinking water, and along with the EPA and various state DOH measurements in milk.

I understand that the drinking water EPA MCL for I-131 is 3 picocuries / l, but that in the US it seems that milk falls into the food category with a much higher DIL (Derived Intervention Limit).

While Japan lumps milk and water both into the 3 picocuries /l max, or 1/3rd that for infants, pregnant women.

Any thoughts on if milk should be considered as soluble as drinking water (as in Japan), or the way the EPA categorizes it, as food?

Thanks for any info.