If the water in Tokyo isn't safe for infants, does that mean it's safe for children? teenagers? others?

It probably isn’t great for anyone at all, but infants are most likely more susceptible to the radiation in the water.

Radiation has its largest effects on rapidly developing cellular systems, such as fetuses, infants, and children, in that order.

Here’s the article:

http://www.washingtonpost.com/world/japan-issues-radiation-warning-on-11-vegetables/2011/03/23/ABbMLTGB_story.html?hpid=z1

It’s not a question of safety really, it’s that infants are still developing and are a lot smaller.

Developing organisms have more cells splitting and growing at a more rapid pace. If something gets messed up in the cell then you’ll have a mutation, which will more easily spread due to the constant growth of an infant.

Also, infants are small so any amount of radiation or other harmful toxins will both have an easier time spreading throughout the body due to the smaller area needing to be covered and the fact that they constitute a higher percentage of what is inside the infants body. Sort of like how a 90lb person takes less alcohol to become drunk than a 300lb person

Infants are less safe for several reasons. One is how quickly their cells are multiplying and dividing, and two they have more years to live. Most cancers develop over time. If a cancer will take 50 years to show itself, then an infant will get cancer around the age of 50. If a 50 year old is exposed to the same chemicals, he probably will not live long enough to suffer from cancer.

I would say that it isn’t safe for anyone.

Look at it like this; some insects and animals have a bite that is lethal to creatures their own size our smaller yet harmless to humans. The average infant weighs less than my cat while I weigh about twenty times that, as does the average adult. Just by sheer size, adults are more tolerant of foreign agents.
Compound that with the fact that infants don’t have a fully developed immune system yet anyways and you can see how they can be harmed by things that wouldn’t faze an adult. That is on top of the aforementioned issues involving cellular division due to growth.

BTW, those who are paranoid about this may want to take a closer look at their own water and diet. Just saying…

Radioactive iodine-131 has a half life of about 8 days.

@mattbrowne I guess that is “good” news, as long as the reactor doesn’t continue bleeding out more radioactivity.

Unfortunately @skfinkel it seems that it does in unit #3.