Curious,
Long story short, all water and seafood that is available is safe at the moment.
As for tap water, for most areas in Japan it was always safe for everyone.
For example in Tokyo, infants prior to 1 year old were advised to consume bottled water on the 23rd, although it was still okay to to consume tap water (but infants were/are always advised to avoid direct tap water anyway). On the 24th the measurements were safe again and the restriction was lifted.
In IIdate Village, Fukushima Pref. where radiation was reported to be most harsh, tap water was restricted during March 21st to April 1st, but is now safe although infants are still advised to consume bottled water to be on the safe side.
I heard a specialist saying on TV that the tap water contamination happened due to rain washing off the first air contamination. There were explosions and fires in the plants back then but there aren't any more, so that makes sense.
In Greater Tokyo, most adults are and have been drinking tap water with no hesitation.
As for seawater, on April 2nd the people at the plants finally found where the contaminated water was coming from and now they are trying to block it.
As for seafood, for example, a March 29th news report tells us that Kanagawa Prefecture tested the seafood being caught and no radiation higher than the standards were reported. These seafood came from Tokyo Bay and Sagami Bay which are big fishing areas for Greater Tokyo.
At the moment, some vegetables and milk from the plant area are restricted from being shipped out of their farms, and that means they're not at all available for ordinary consumers. But the news today tells us that they are soon to lift that restriction as well.
It's unfortunate that even the safe foods are being avoided due to rumors. People are trying hard to promote its safety. For example, on April 1st, they held a vegetable market in the middle of Tokyo using radiation meter as a demonstration. The shopkeeper measured a 6 months old girl's coat which turned out to be 0.6 microSv and then measured rice from Fukushima Pref. which turned out to be 0.5 microSv.
Sorry that the sources are in Japanese.
http://www.yomiuri.co.jp/national/news/20110331-OYT1T00975.htmhttp://sankei.jp.msn.com/region/news/110329/kng11032921500006-n1.htm
http://www.sponichi.co.jp/society/news/2011/04/02/kiji/K20110402000546...