Would you tell OP to use tap water if located in flynt michigan?

Point is, OP doesn't know what's in the tap, website isn't saying what's in the tap. I wouldn't use it until I knew what was in it, now if you can't light your faucet on fire, 99% of the time you would be fine. I just like knowing what I'm giving my plants

The OP is talking about flushing with pure water immediately after the tap water. Under those circumstances tap water quality doesn't matter much in the US since the exposure is so brief.

I was talking about half-lives or exponential decay. It also applies to fluid or gas displacement. The minerals in tap water are soluble. Those that adhere to the clay tightly don't come off easily. Flushing well with pure water after watering with tap water is a way to remove most of the minerals in the tap water.

Why use tap water at all then?

---------- Post added at 02:00 PM ---------- Previous post was at 01:59 PM ----------

And OP posted wanting to use more tap than rain

The tap water will have run out. As long as the rain added is enough to run through the pot, then out the holes, yes, that will flush out most of the solutes.

Most of the US has tap water that's adequate for most of the orchids people grow. Yes, most grow better with fewer dissolved minerals, but more frequent watering in more open media helps a lot.

Using the term "tap water" is not particularly useful... in some places, the tap water is very low in solids... San Francisco and New York are well known for excellent tap water, there are many other places too where the source is snow melt and it runs over granite. Other places, it's "liquid rocks" ...true in much of southern California and I am sure many other places, where the water is in contact with limestone-type (calcium carbonate) rocks... areas that likely were ancient seas. But watering with that stuff (if not too horrid) solves the problem of calcium deficiency. (I had not even heard of that being a thing until seeing on the Orchid Board that some people need to supplement calcium in their tap water... where I live, calcium is free and plentiful) Of course with RO, if you take all the minerals out, you do have to add a bit back... and one way to that is to mix some tap water with one's very pure water. So that gets down to the basics... What are the components? What is the goal? Without some quantitative information the "tap water" vs "??" discussion is not particularly useful.

Agreed

there are wells around here that make you clean your coffee pot every month and peel the calcium scale out of it. it comes out in sheets. solid rock

I picked up some tiny corks on Amazon to plug the holes. I flush a bunch that way.

Is 77 too hard to use for flushing?

77 what?

If that is the true dissolved solids content, that’s fine. If that is the alkalinity, as ppm CaCO3, that’s still OK, but not so great.

Sorry. 77ppm. Can I safely flush with it? Thanks Ray.