There are water fountains located all through the game. You must use every water fountain in the game. You can load back to previous checkpoitns and collect each fountain, you must progress onto the next checkpoint once you use the fountain so the game saves your progress.
If the achievement doesn't unlock while collecting the last fountain complete the game or finish the last boss fight and it will unlock.
To see pictures of all the water fountain locations, check out the achievement guide for Ghostbusters HERE.