Reactivating the water grid sounds like an idea kevin would kill pretty quickly. I’m thinking of something much more limited that a group of people could construct. You would have a central water tank, a pump, a simple filtration system to reclaim water that can be re-purified, and a septic tank or cess pit.
As for the actual mechanics, I’d say the piping would not be manually placed, but rather accounted for by “connecting” a shower or something to the network, an action which requires pipes equal to the linear distance from the tankage and filtration/septic system.