Japan crisis: Radiation in Tokyo water 'a blow'
23 March 2011 Last updated at 07:57 GMT
Officials in Toyko have warned that children under the age of one should not drink tap water because of radiation levels in the city's supplies.
Iodine levels in some areas are twice the recommended safe level.
The BBC's Chris Hogg in Tokyo said that news of the water pollution would come as a blow to the Japanese government, but would not spark panic.
The authorities have also imposed new restrictions on food from areas affected by leaks from the Fukushima nuclear plant.