Japan estimated the cost of the damage from its devastating earthquake and tsunami could top $300 billion as authorities in Tokyo warned that babies should not be given tap water because of radiation from a crippled nuclear plant. The first official estimate since the March 11 disaster covers damage to roads, homes, factories and infrastructure, and dwarfs losses from both the 1995 Kobe quake and Hurricane Katrina that swept through New Orleans in 2005, making it the world’s costliest natural disaster.