As I mentioned in that earlier thread from 2008 [[emphasis is mine):
From page 5 of the Detroit Water and Sewage Department - the First 300 Years:Early Water Mains
Tamarack trees were harvested from marshy regions along the Clinton River before being rafted down to Detroit. The logs were hollowed out and laid end-to-end along Jefferson Avenue and parts of Larned and Congress. Individual sections were joined together with smaller sleeves, most frequently made of lead.
The term fire plug - slang for a fire hydrant - originated during this period. Crews responding to fires, exposed and tapped into the wooden main to connect their hoses. When finished, the crews used a plug to seal the hole.
Work crews continue to find wooden mains. The quality of workmanship that went into these early mains was superior. So superior, in fact, that most would still be perfectly functional today if the pressures of modern water systems were not so high.
In other words, there are not any wooden water mains still in service - if they were, they would be continually breaking because of the higher pressures used today. The old wooden water mains were abandoned in place when they were superseded by new cast iron water mains. It's the abandoned wooden mains that are still being found when repairs are being made to adjacent utility lines.