The news that Japan is worried about the amount of radio active iodine isotopes in the drink water of Tokyo must be the understatement of the millennium
Just so you know for drinking water to become so contaminated that it becomes a health hazard radio active particles have to land in it. In Japan that means the particles had to have been airborne. In fact according to Lanthanide who comments on the Standard the distance over which those particles would have to be transported a significant explosion if nuclear bomb type strength would have been needed, in fact here it is from the man himself:
For significant amounts of radiation to reach Tokyo, which is quite far away, radiation would need to reach very high into the atmosphere. This would require much more than the current hydrogen explosions, you would need something on the order of a nuclear explosion (as in, atomic weapon explosion) which requires the fuel to reach super-criticality. Weapons grade uranium, the type required for an atomic bomb, is 90% U235 enriched. The type used in nuclear fuel is only 3-4% enriched. Super-criticality simply isn’t going to happen, unless somehow all of the U235 managed to get itself together in a lump. Even so, nuclear weapons explode the way they do because of very precise engineering (perfect spheres of fuel, ‘gun’ ignition systems etc) to ensure super-criticality is reached before the fuel can blow itself apart, such a physical arrangement of fuel happening by chance in a reactor is practically nil.
The distance between Tokyo and Fukushima is 238.34 km to be precise and the amount of particles in the air must have been quit high for enough particles to land in the water to make it unsafe for infants to drink.
What this means is that there are enough particles in the water for a significant amount of infants, who are much more susceptible to the destructive effect of radiation because their bodies are growing and there is an awful lot of cell activity going on in their tiny bodies, to become contaminated with the radioactive particles.
What this also means is that there are an awful lot of particles floating in the air which can be breathed in by everybody and which in the future will cause cancer. The radioactive particles are iodine which has a half life of some 8 days and which when inhaled have a tendency to be absorbed by the thyroid causing thyroid cancer.