The entire farm was about the size of an ice cube tray, and had a growing volume of about 2 cups. Terrariums in general would use about 6 tsps for a 2-cup terrarium; the Chinese experiment used about 3.5 tsps. I'm not sure why they used that amount of water; I would speculate (and it's only speculation) that the plants they choose didn't need more, or possibly the lower gravity on the moon meant that the water was generally more accessible to the plants.