10,000 Gallon Cisterns

I have mentioned that we are capturing our rainwater from the roof of our building. This captured graywater or "free" water will be used for irrigation and in other water saving ways. In between the classroom wings there are six 10K gallon cisterns buried beneath the commons.
I have been asked "how" we capture this water from the roof. In an ordinary roof drain the water flows down the gutter, to the downspout, and out the drain. We will capture from the roof, to the gutters, then our downspouts tie into a roof leader below the surface grade, around a perimeter storm drain pipe system and into the cisterns.
They were being fitted with tiedowns to the concrete anchors in this photo. They will be surrounded with gravel and fill.
At any given time, we will have 60,000 gallons of "gray water" or captured water available for recycling!
How big is a 10K gallon tank? This photo shows the scale to human size.
One of our "sustainable" features in the new high school. :-)