Ah yes, fallingsand.
That game does some amazing stuff with particles; I believe in one version, you can mix water and salt to make salt water.
And then, with the right placement, you can purify the water. First person on the forum to take a screenshot of a water purifier gets an E-cookie.
EDIT: There are multiple versions of this game. Most likely, you'll have to search around for the correct version to purify water. >_>
All the versions.