Nasa has confirmed that the toilet on the International Space Station has failed, leaving astronauts in an urgent need for spare parts.

The problem lies with the fan that draws liquids into the waste chamber prior to being ejected to burn up in the atmosphere.

At the moment solids can be handled by the Russian-made toilet, but liquid disposal is proving impossible.

"Like any home the importance of having a working bathroom is obvious," said Nasa spokesman Allard Beutel.

Waste disposal in space has long been an issue, since gravity-fed toilets do not work in orbit. Instead the waste is sucked from the toilet by air pressure.

Space Shuttle Discovery is due to bring the next module for the Space Station into orbit on Saturday, and officials are considering adding replacement parts to the toilet during the mission.

However, at this late stage this may prove problematic as the load on the Shuttle has already been packed and weight distribution is critical on the flight.

There also may not be room for new equipment, since the Shuttle is carrying a 14,500kg Japanese laboratory which is so large that the Shuttle's robotic arm has had to be removed.

This is not the first time that Nasa has suffered problems with orbital plumbing. In 1984 Shuttle astronauts were forced to urinate into plastic bags and store them on board after fears that an improperly working toilet was causing icicles which were damaging the heat resistant tiles.