Chapter 9- BRINGING THE TREE BACK TO LIFE

Return to the underground maze and go back to the water tank. Now that you have opened the lower valve in the pipe room, the tank is drained. There's a ladder going down to the tank's bottom. Its upper gate is no longer blocked, and you can descend it.
At the bottom, there's a big lever. Push it and the massive iron panel will slide open: it turns out this panel was a gate valve.

Now, you can pass into the culvert you reached from the leftmost door of the 3-door room. You can once again see the dead tree through the grating, but there is still no water flow here, since the water flowing to the tank is still routed toward the city and the desert.

Return to the lower scaffolding and pull the lever. The valve closes, the spinner in the observation portal stops, and the water rises again in the tank. Now that you have opened the door at the tank’s bottom, water returns to the creek and flows past the tree.