Seems a bit odd. You got talked out of buying a PPM meter, and given that you were talked out of buying it this must mean you agreed with his reasoning for not owning one. So why bother enquiring about ppm's of various waters. That in itself makes it sound like you should have bought a ppm meter (i will be like the hydro store guy and say don't bother, utter waste of money.
It's generally accepted that if you can drink it then so can your plant. Growing cannabis can get as intricate as you want it to be, but it's a plant, it will grow in just about any conditions and people just get far far too anal about this that and everything. A large number of very successful growers don't even bother PH'ing their water despite what all of these fancy nutrient ph charts dictate and they don't have an issue.
Cannabis growing is becoming like anything else in life, people are producing anything and everything and finding a way to persuade you that it is a requirement for growing. Water, air, nutrients and light, all you really need