| Small Pipe
The water does dissipate after 39 tiles max. If the water pressure is low in the large pipe (i.e. the large pipe is too long), then the range of the small pipes will decrease.
Prisoners cannot escape through small pipes, as opposed to large pipes.
Pipes can not be built through a Perimeter Wall (or Water), and building a Perimeter Wall over any existing pipe will remove it. It is not possible to build a small pipe over a large pipe. The large one has to be dismantled first.