Meredith Moore, Sustainability Programs Manager, reached out to Associate Professor Ashlynn Stillwell to ask a question from the AASHE STARS sustainability report (Association for the Advancement of Sustainability in Higher Education, Sustainability Tracking and Reporting System). The question is: "Has the institution calculated a natural water balance for the campus to assess the sustainability of its water withdrawal?". Professor Stillwell replied explaining that UIUC has not calculated its natural water balance, and proposed ideas on how to it can start doing so. Specifically she said, 

"First, it seems like a question that is motivated by water scarcity, given the phrasing "sustainability of its water withdrawal". Extraction (withdrawal) of water is not the only way I personally would calculate water sustainability. In our part of the world, runoff volume and the contaminants contained in that runoff are important aspects of sustainability too. 

Next, to actually calculate the natural water balance, I would think one would write a high-level mass balance around the campus. 'Natural' to me implies 'non-engineered', so at first pass, I would only include natural water flows. However, the question then mentions waer withdrawal, which is a non-natural human interaction with water, which makes me think the engineered water system should be included also. 

For a high-level water mass balance around campus, it would be similar to any mass balance: IN - OUT = CHANGE IN STORAGE 

What goes IN? potable water, raw water (?), makeup to chilled water loop, makeup to steam loop, rainfall, runoff from upstream areas, inflowing streams, inflowing groundwater. 

What goes OUT? waste water, evaporation (from steam and chilled water loops), evapotranspiration, runoff (from rainfall and from overwatering from sprinklers), runoff to downstream areas, surface stream discharge, outflowing groundwater.

How much is CHANGE IN STORAGE? probably zero at steady state on a sufficiently large timescale."