One Utility Network multidomains vs multiple UNs

[xyz_AL]

Hi all,

I've to build a Water, Sewer and Stormwater UN system. The service territory for the three networks is the same, and some structures are also shared between water/sewer, sewer/stormwater, water/stormwater.

I think I've two possibilities (I apologize in advance but I'm quite new at this data model so maybe I could say something wrong): one UN with 3 domains sharing the same structure or three separate UNs.

I wonder what solution could be better, considering that the 3 domains will be all managed by the same Authority.
However, if for example the Trace tool (but also many other UN tools work on 1 domain) can run on just one domain at a time the user will have no possibility to do any cross-check between different domains, even if they share some structure elements.
And what about topology? Disabling it, enabling it and validating it can be very time consuming on large geodatabase.

Nevertheless, it is also true that many shared structures will be replicated if I setup three UNs and so the effort to maintain the three systems updated on the same structures will be great (and cause of errors).

So, the UN Esri model is a great tool to manage the utilities and I know that the model is supposed to do its job at the best by integrating more domains together, but, if so, however I don't understand well why some UN tools can't work on multiple domains sharing the same structure.

Is it correct what I'm saying or I'm completely out of the way? Could you please help me better understand the best way should I use to integrate the three UNs? Thank you in advance.

[AneteZvaigzneLV]

I am also quite new and eager to understand this. Maybe @AlixVezina can give a comment or tag someone from the team? Cheers!

[MikeMillerGIS]

Modeling 3 domains in 1 UN will provide the ability to share structures and trace through domains.  The only tracing between domains at the moment is Find Connected, which does not use the domain parameter.  You can chain traces, such as a downstream water trace, get it results and add flags there and then an upstream Sewer trace(can do this with two UNs too).  

When modeling multiple domains in the same UN, the only item you need to be careful about is how many inline network attributes you use as there is a limit(21) to how many bits you have. 

Another note, when modeling multiple domains in the same UN, all those layers/domains are required to be in the feature service.  So permissions are set at service level, so if you do require User A to only edit Sewer and User B to only edit water and manage the Utility Network capabilities, you do not have this level of permission at the service level.