Salt water

Pescatons survived on salt water. (AUDIO: Doctor Who and the Pescatons)

Dr Francis Augur used salt water to kill the Keratin. (AUDIO: The Glittering Storm)

In the fifth parallel universe that Rose Tyler visited in her attempts to return to N-Space, an automated mining ship was teleporting the salt out of the oceans' water, purifying them. (AUDIO: Saltwater)