There’s a lot of bullshit and confusing statements about the level of radioactivity in tap water in Tokyo.

Here is what Mainichi Shimbun says: “The intake limit set by the central government is 300 becquerels per kiloliter of water” (they are talking about iodine otherwise the statement is pretty much useless).
Now the New York Times: “The recommended limit for infants is 100 becquerels per liter. For adults, the recommended limit is 300 becquerels.” I assume they mean per liter.
So are we talking about liters or kiloliters ? For me, there is a big difference.

Now, for more nonsense: “Another reassuring fact: The reported radiation dose in Tokyo tap water (210 becquerels) versus the Japanese safety limits (100 becquerels/liter for infants, 300 for adults) is not far from the difference in radiation dose people naturally get if they live in a place like Denver versus a sea-level city such as Los Angeles. That’s because the thinner atmosphere in Denver provides less protection against cosmic rays.” (npr article).
What are you talking about ? Becquerel is only a measure of the radioactivity that is not directly related to the energy and cannot be directly used to evaluate the effect on health  !

Now, let’s look at some data (http://atmc.jp/water/): In Tokyo, on 3/22, the graph says 19 bq/kg of Iodine 131 in water. Assuming 1 liter of tap water is 1kg, it means 19000 bq per kiloliter. On the same page, it is written that the limit for infants is 100bq/kg… It seems that the correct unit is kg or liter rather than kiloliter, most articles use bq/kg or liter. Still, So, where does this 210 bq/kg figure come from ?

Even more confusing: bq/m2. That is radioactivity for a surface. That is used for radioactivity in rain. Again, let’s have a look at some data (http://atmc.jp/ame/). On 3/22 in Tokyo , 36000 bq/m2 (iodine 131)! Does it depends on the quantity of rain that fell on the same surface ? If we assume 1cm of rain, then the volume on 1m2 is 0.01m3. The volume 1l of water is 0.001m3. So, the 36000bq/m2 are actually for 10l of water, that is 360bq/l or 360bq/kg… Higher that the limit of 300bq/kg but that is for 10mm of rain. Does this calculation actually makes sense ?