Winter Urban Garden: I have no idea how to water

Dateline: 2015-12-17 The GreenStalk Garden System that I’m using provides many cool features, including a handy water reservoir. As you can see from the image it provides markings for how much water to add based on the number of tiers your using. The only problem is that it also has a sizable drain to flow down to the lower tiers. Filling it up to the “5” mark is almost impossible...