Engineers often work on projects in areas where they have not worked before. When that happens, how do we decide whether the incoming water should be used as-is or treated for domestic use? Should it be softened? Should only hot water be softened? Should soft and raw water be blended? If so, in what ration? Is RO needed for some applications? This presentation introduces a spreadsheet that may become an ASHRAE tool offering that will help engineers to make those decisions based on something more than what the building next door does.