It's not clear to me what the source of water is relative to the size of the forest, because IIUC, in dry regions like Egypt (and California, Israel, etc), unless you use drip-irrigation with targeted crops (which won't grow a forest), agriculture requires a huge amount of water compared to domestic water consumption, so the wastewater stream from the latter intuitively can't be nearly enough to support a forest.
Perhaps they are drip irrigating the entire floor of the artificial forest to minimize evaporative losses? The paper linked in the article [1] doesn't really explain how they are doing this.
EDIT: this article [2] explains the system in a bit more detail. For a sense of the scale of forest vs the wastewater supply, it's a city of 400K people whose wastewater is supporting a .78 square mile "forest". So it's really more like a large park. It's a great demonstration nonetheless, especially if it can be a productive source of food for the city.
Perhaps they are drip irrigating the entire floor of the artificial forest to minimize evaporative losses? The paper linked in the article [1] doesn't really explain how they are doing this.
EDIT: this article [2] explains the system in a bit more detail. For a sense of the scale of forest vs the wastewater supply, it's a city of 400K people whose wastewater is supporting a .78 square mile "forest". So it's really more like a large park. It's a great demonstration nonetheless, especially if it can be a productive source of food for the city.
1. http://www.fao.org/forestry/35800-094f4eedb0c86a4a33be1a3d90...
2. https://www.intelligentliving.co/egyptian-desert-forest-recy...