Updated March 24rd 18:08
Restriction on use of tap water for infants has been lifted, as the level of radiao active iodine at the drinking water treatment plant has dropped from 210 Bq/kg to 79 Bq/kg. Temporary health standards of radioactive iodine set by Japanese Government is 100 Bq/kg for infants under 12 months and 300 Bq/kg for adults.
The most updated information on tap water in Tokyo can be found here
Elevated level of radio active idonine has been ditected in Kanto area on March 22nd.
Residents of following area are adviced not to give tap water to infants, especially babies less than 12 months old. Tap water should not be used to prepare milk nor baby food.
These municipalities are distributing bottled water for the families with infants for immidiate use.
23 Special Wards(２３区)
Machida City (町田市)
Tama City (多摩市)
Inagi City (稲城市)
Hitachi-Ota City (常陸大田市）
The level of radioactive idone is low enough for other usage including drinking, cooking, and bathing. It is a precautionary action and does not impose immidiate health risk.
You can find the radiation level in air, tap water, and rain at this website
This website provide information about radiation risk in Japan in 日本語 | 英語English | 中文 | ベトナム語Tiếng Việt | 韓国語한국어 | ベンガル語 | ロシア語Русский | ペルシア語Fārsī | ドイツ語Deutsch | イタリア語Italiano | ルーマニア語Limba română | フランス語Français | ポルトガル語Português | スペイン語Español | タイ語ภาษาไทย | タガログ語Tagalog | インドネシア語Bahasa Indonesia
I will be making an update on this.