Smoke on space station came from water heater

 A kitchen water heater is being blamed Wednesday for smoke aboard the International Space Station (ISS).
Russian astronauts reported smoke and a burning smell in their main compartment Tuesday, but there was not enough smoke to trigger alarms or to warrant the use of masks by the six-man crew. The smoke came from a vent and dissipated within a half-hour.
The astronauts quickly disconnected the electric water-heating unit and activated air purifiers in the Zvezda (Star) compartment.
ISS commander Steven Swanson said there was only a small amount of smoke, and everybody was fine.
On Wednesday, astronauts installed a spare unit, and the National Aeronautics and Space Administration (NASA) says it is working normally. A similar problem occurred in 2009.