When entering into a national phase in the US, how should claim X in the following example be amended?
Claim 1: “A system for watering grass wherein (…)” Claim X: “A golf course comprising an installation of the system described in claim 1.”
What follows here under should not be construed as legal opinion or advice. Without knowing the details, it is difficult to give any substantially strong opinion/suggestion. If your application is in PCT stage and has been published by WIPO, you could have given reference link for the same.
Anyway, USPTO allows three independent claims without any extra charges, provided of course there is integrity of invention. Else, the examiner will direct you for division of application.
For structuring Claim X as an independent claim there is no need to mention system of Claim 1. It can be written as
A system for watering grass in a golf course comprising ......
By doing so, you will be opting for a claim narrower than claim 1.
Maintaining broadness of claim, the application of 'the system in claim 1' to golf course can be made a dependent claim as under
The system of claim 1. wherein the system can be used (at least) to water a golf course .......
By using the term 'at least' you will be able to keep your claim a broad one.
In the US it is required that dependent claims be in the same statutory class as the independent claim it depends from. The classes are process, machine, manufacture, and composition of matter. The important distinction is between "process" and the rest. Methods vs tangible things. They may also care about the distinction between composition or matter and the other objects - I'm not sure.
In your case you have a watering system (a thing) and a golf course (a thing) so there should be no problem with statutory classes.