Pok Fu Lam No. 1 Service reservoir [????- ]

You pass this on the Hong Kong Trail. It's at the top of the steps leading up from the main Pok Fu Lam reservoir.

Nothing very exciting, but there are two rows of cast iron air vents that are quite ornate:

Behind each vent is a small access plate:

And there's this small building at the back:

The building and the plate both use the initials 'W.W.' for 'Water Works', not the 'W.D.' for 'Water works Department' suggested previously.