Judging by the huge cap on that tank, it looks like that would be a water tank. Don't suppose there's a 4th photo that shows the side facing the curb? That would reveal a door for shovellin' or perhaps a fuel tank. A lot of steam engines were oil burners, although I'm not sure when that started without digging around. Gotta get to bed, although I'd much rather be firing that thing up and terrorizing the neighborhood.

Is the tank at this end the water reservoir? And what fires the boiler -- coal? Kerosene? Which goes where?

Based on the sign in the previous photo and the presence of the railroad in this one, this whole area was wiped out by the construction of the Whitehurst Freeway. The Potomac River is on the other side of the buildings to the left; the C&O Canal is about a block north. There was a lot of industrial stuff in this little strip along the south edge of Georgetown, including a transit company power plant and the old Washington Flour mill. The rail line is a byproduct of a B&O attempt to get past Pennsylvania RR control of the Long Bridge (next to the 14th St. Bridge).

[That's the address of the construction company that left the chimney liners there. "There" turns out to be in or near Rosslyn, Virginia. - Dave]