Tokyo Water Bureau officials said levels of radioactive iodine in some city tap water is two times the recommended limit for infants.
The officials told reporters that a water treatment centre in Tokyo that supplies much of the city’s tap water found that some water contained 210 becquerels per litre of iodine 131.
They said the limit for consumption of iodine 131 for infants is 100 becquerels per litre.
They recommended that babies not be given tap water, although they said the water is not an immediate health risk for adults.
Nearly two weeks after the twin 11 March disasters, nuclear officials were still struggling to stabilise the damaged and overheated Fukushima, which has been leaking radiation since the disasters knocked out the plant’s cooling systems.
Radiation has seeped into vegetables, raw milk, the water supply and even seawater in the areas surrounding the plant.
Broccoli has been added to a list of tainted vegetables that already includes spinach, canola and chrysanthemum greens.
Residents of cities in Japan’s north east earlier had been advised not to drink tap water due to elevated levels of radioactive iodine, which can cause thyroid cancer.
Until today, levels found in Tokyo tap water had been minute, according to officials.
The US Food and Drug Administration said that it will halt imports of dairy products and produce from the Fukushima region.
Other foods imported from Japan, including seafood, will still be sold to the public but screened first for radiation, the agency said.