An atmospheric condenser is a device that can extract water from the air.
Kamin, a resident of Kataan, suggested building atmospheric condensers to fight the constant drought that was affecting the planet to his community's administrator. Each community would be responsible for its own condenser, as the project would be a monumental undertaking.
When it became clear that his atmospheric condensers wouldn't be built, he decided to build his own with his friend Batai. (TNG: "The Inner Light")