I made the wrong reference. Its the Strata Schemes Development act 2015 Part 1 Preliminary 3 definitions
I think the section you’re referring to says “the pipes, wires, cables or ducts that are not for the exclusive benefit of one lot …” If not, please advise.
The question arises, is a valve that is used to isolate the building’s water supply from the lot part of the overall infrastructure or “for the exclusive benefit of that lot”?
Your unit’s front door, which isolates your lot from common property, is common property. It’s not a perfect analogy but it illustrates the issue. Similarly, the isolation switches and fuses on your power board are common property, even though they are connected only to the specific units concerned.
The memorandum says the stopcock is common property and I can see nothing in the Development Act that contradicts or supersedes that.
More to the point, this problem, with the whole building’s water supply having to be shut off so one unit’s leaky taps can be fixed is a perfect illustration of why that is the case.