If tap contains any phosphate we can be sure Ortho & Poly phosphates are being dosed from municipality.
This will bind bicarbonates & carbonates and will not break down to GH unless pH levels are over 9.0
Definitely not an issue, one would just see PO4 around 1ppm from tap.
Is this PO4 available for plant uptake, I can't say.
Since mostly surface water is being used the options are calcium hydroxide and or sodium hydroxide to raise pH for the EPA requirement for piping degradation.
Municipality pH targets are running @ 7.5pH and the lime is used as the norm.
If NaOH was used the sodium content would be minimal and not affect plants.
This is all I have from the visit.
Would need to re-read this thread to comment further.