Which is the best way to describe watering facilities?

Building plants to provide irrigation, is a matter of engineering.
The precise branch is hydraulic engineering, which belongs to the civil engineering area. As a matter of fact, it is possible to uniquely describe a facility or a system, with a document. A report is used to describe modifications, tests, or maintenance. For the system as a whole, a project relation would be the reference.
Here is an example from a project to improve the Crow Irrigation Project, located in North America, USA.