Create a lake or a beach front on your planet. As of server 3.0400 generates a small amount of food (algae), ore (whatever kind a mine on the planet produces), and water.
A complete set of beach tiles is given to anyone who sends out invitations and gets 10 or more people to sign up. Even if you don't particularly want a set of these tiles, they are a useful trade commodity.
This tile can be constructed at the Archaeology Ministry using a gypsum glyph and an anthracite glyph.