Yes, the Tres Peidras tank is still standing, I (like KevinM) drove by it going to and from the MOW special.
But the tank is very much worse off in recent years. See my Sept 2008 photo. This is as close as I could get.
By comparison, it now looks like the tank is twisting with large gaps in the wall staves, and about to collapse in on itself, . The roof is in effect slowly crushing the tank wall.
It's definitely on private property, behind a substantial fence and gate where there is also a residence.
Bob of AZ