A water supply is used to continuously provide a greenhouse with water. You place a water supply connected to a base in which you have a greenhouse, then drop ice onto the water supply (you'll see the little meter on the side go up). The greenhouse will slowly consume water stored in a water supply over time.
I've recently been working on an automated Repair Drone that will fly around and fix leaks! Will be in the next update (once it's ready, still has bugs to work out). Preview video: https://twitter.com/cairn4/sta...
