Thanks for your response,

We have an electric 40 Gallon hot water tank (rental) that presumably
is 6 yrs old (age of the house). All filtering happens before the hot
water tank.

We had posed the possibility to the rentor (local utility) but they
"blame" the water treatment system (with the statement to the effect,
we see this all the time it usually is the water treatment system).
What would be the best approach to determine "blame" in this case.