Tap water EC + Nute EC or just Nute EC?

I know there is another thread about this open but people have gone off topic and i would like some sensible replies.

What do you guys who use tap water do? Take away the base EC of your tap water or take the value of water EC + nute EC to get your total? I have been doing the latter but i am wondering if this is not the best option. My base EC is pretty high. Just wondering if my plants are getting what they really need.

Please, no comments about RO, if i wanted RO i would have got it by now. Thanks.

I always add the two, I use the total for my reading, there's a lot of pros and cons on this and I too whould like to have a true scientifical answer. hope some expert can chime in with good credentials.