My project building is very new and operation started from 2008 onwards. All the plumbing fixtures and fittings are high-efficiency ones meeting the IPC baseline standards. However, we had retrofitted certain fixtures & fittings aimed to achieve more percentage savings.
First of all, is it required to document the policy mandating an economic assessment of conversion to high-performance plumbing fixtures and fittings as part of any future indoor plumbing renovation?
In my case, even I have the policy but how can I account disposal cost and maintenance cost savings? Is it really required to satisfy the pre-requisite?
How can I approach this problem? Has anyone else had to deal with this?

I would like to recommend the minimum it would take to get my client to meet this prerequisite, but how can I do that? Thank you for your help.