I don't pH with soil. That is a coco/ hydro thing unless you have issues.
I some do pH and EC with soil, I don't.
That being said to know your numbers as a baseline is valuable.
I would use your tap [ I think you're in good soil ] for watering to start.
I never EC but understand. When you measure you want your base water to be 0 [ again this is hydro].
Some just say that their tap is 0 which in your case would mean to add to whatever level you choose plus 223 for your tap. You want 500EC you mix you ferts until you get 723EC using your tap.
This is my water which really worked pretty well for me in all grows.
pH 7.6 / 350+ TDS
I know if you need to use 'clean water' then you want the distilled or RO.
Before I went full bore with either if I had trouble I would try mixing tap and distilled or RO like Mosh mentioned.
If you have 0 TDS water pour it through your soil to run off and test pH and TDS/EC. Compare [ right down] the pH change and EC/TDS
Those numbers are what your soil only contains so when you add ferts and test the run off you will know what they should add up to.
This way you can see if the plant is using the ferts or they are still in soil.
This is a great help when a plant has issues.
Hopefully after getting baseline numbers you will never need to test again, but if you do you will be able to know what you see and report to us dummies what is going on.
I do none of this. I try to water completely to minimal run off.