Had a water filtration salesman come to my house yesterday

I was wondering if you guys knew what the chemical he used was and if his pitch was bogus, my water is handled by a third party company and tastes fine.

So essentially, he took some of his "treated" water and some of my tap water dropped in what I swore he said was potassium hydroxide (drain cleaner?) both samples became cloudy (as if drops of white food coloring were dropped) but over the course of 3 minutes or so his water cleared up, while my water stayed cloudy, then he explained this is a clear sign of heavy minerals such as lead, among his other tricks I found this to have the most effect on me and I'm trying to figure out how he did it.