Pure Water v Hard Water. Well, a paper with that title wouldn't look so great on a resume so the official title was "The Tribological Effects of Metal Removal Fluids Diluted with Purified Water vs. Hard Water." So - hard water vs pure water - a no-brainer right? It's well known that as the hardness of the water increases, so does the number of issues with the metalworking fluid. Water makes up 80-97% of the metalworking fluid system. It's generally known that pure water increases the life of the metalworking fluid system. But that's not the end of the story. Presented by Alan Cross, Senior Project Engineer of Houghton International, the study mixed pure water with hard water to compare five different fluids, four metals, and three water hardness levels. As expected, pure water systems has many advantages including easier mixing, smaller particle sizes, improved wetting and penetration, reduced residues, improved filtration, less carry-off, greater bacterial and fungus resistance, reduced corrosion, reduced mist and concentrate requirement, and better overall stability. That's a long list. However, torque test performed in this study corroborated field reports that certain elements of performance suffer in a pure water system. In particular, pure water systems may lessen tool life and increase foaming and levels of entrained air. Why the negative tool life impact? Because ions of calcium and magnesium in hard water form soaps that provide lubricity. Still, I'm thinking about that long list of advantages of pure water and I'm always interested in reducing the number of problems in my life. A well performed study and an informative presentation that helps prepare the end user.