Aqua's Support system has the ability to allow users to be associated to multiple companies and thus the ability to for the user to open cases against a different company. This is common for our partners who are working with many different companies or sites. These users should work with the companies Customer Success Managers to enable this feature on their users. 

Once enabled, when opening a support case the user will see a company drop down where they can select which company the case is opened under. 

When you need to review opened/closed cases there will be a company selector for the user as seen below.If your user doesn't have these options then you are not setup for multiple companies