This is a question that has ...
Published by Terry Scheurman, President at Applied Specialties, Inc.
This is a question that has a number of answers based on what the Professional is tasked with doing and the industry in which they operate. Since the tasks may be so far spread as well as industries so diverse, I don't think there could be a perfect kit.
However, there would be one old stand-by that everyone should have and it would be a titration kit to run alkalinities, Hardness, pH and conductivity. I happen to prefer ones with small burettes that permit the use of generic reagents. After this, add-ons for PO4, SiO2, Fe and on are all an industry or task specific need.