If you look at the USGS map there is possibly a dammed up pond and structure along the old railroad grade after it crosses the Mt Clinton Road. This is incidentally a numbered USFS road. I would agree that its probably tied with the hotel complex. I think its A surface water source from a brook so its cannot readily be used as potable water unless expensive water treatment is installed, but it could be used for irrigation. The pipe was abandoned with sections missing for several years and at some point it was repaired for a few years. At one point there was a lot of new green PVC piping materials piled in the woods along Jefferson Notch Road to presumably rework the intake but a subsequent flooding event seems to stopped its use. In theory the infrastructure outside of the state of NH owned right of way would need to be covered with a USFS special use permit subject to renewal if it was in active use, if it was abandoned than its probably old enough to be an historical artifact. My guess is the FS looked the other way when it was put back in operation.
Given the type of pipe used it could hold considerable pressure which may imply a hydro generator but subsequent temporary repairs implies its now running at low pressure. The entire hotel complex had to generate its own power at an on site power plant that still exists as I suspect public power took quite awhile to make it to the hotel so possibly like the auto road complex they had a hydro electric generator fed from this source?
The cog has at least two abandoned steel intakes that cross onto USFS land.