Does anybody know where USGBC / WE TAG came up with Table 1? I've not been able to find it anywhere, except where it is referenced as coming from LEED. For example, the EPA WaterSense Water Efficiency Management Guide for Mechanical Systems linked below has the table, but cites the source as LEED. This credit is really poorly developed / explained in the LEED Reference Guide and over they years they still haven't addressed many basic technical questions. It also doesn't have any good citations or reference standards the way most LEED credits do. All of the federl / non-vendor best practice guides I can find talk about maximizing COC and monitoring conductivity, but don't include suggested maximum concentrations.

The reason I ask today is we have a large office site with cooling towers in Illinois and the water treatment vendor says conductivity of 2,000 μS/cm is too high. They won't push conductivity past 1,350 μS/cm stating that anything higher causes scaling on our heat exchangers, reduces efficiency, etc. We're currently at 4.5 COC and would save a good amount of water if we set our conductivity limit closer to 2,000, but we'd have to ignore the warnings from our vendor and absolve them from responsibility for scaling.

https://www.epa.gov/sites/default/files/2017-12/documents/ws-commercialb...