Is there any non-invasive way of identifying the existence of galvanized steel pipe in plumbing system (other than the tell-tale rust colored water) when the pipes are buried in finished walls or floors? I had read somewhere that a process existed which allowed a properly equipped person to measure the electrical conductivity of the pipe to determine if steel pipe exists along the run (steel and copper conduct differently).
A house that I inspected yesterday had a long-unused second floor bathroom and a tub in a separate room that delivered rust colored water (hot side only) when first turned on and for a couple minutes thereafter. (classic sign of steel pipe). However, the visible supply pipes throughout the house, including the unfinished basement were all copper.
The regularly used faucets didn’t show any color that was visible to the eye. There was no visible staining inside the 10+ year old dishwasher on the main floor of the house.
Note that the water heater is old (23 years) so rust in the heater tank is another possibility.