You seem to be making a mountain out of a mole hill here. Trying to draw some type of â€œreasoningâ€ of routing a water line next to a steam line is stretch of good piping design. â€œIFâ€ youâ€™re trying to use the heat on the steam line to keep the water line from freezing then the two lines would be banded together and in the same insulation jacket â€¦which is rare! The more basic premise is â€œhow to handle insulated linesâ€ â€¦and I state again, insulated lines on shoes are easier to deal with than those insulated line that have no shoes! â€¦NO matter what the commodity is.
The other question that seems to be popping up is why insulate a water line? â€¦I can think of two right off the bat here, first (as already stated) to keep it from freezing and the splitting the pipe! This could also use the addition of some type of heat tracing â€¦pretty standard practice. The other reason youâ€™d insulate a water line is to keep the water from getting too hot! This is what we do around here on potable water lines that feed eye wash stations, that and buried reservoirs. BUT all this is dictated by the process people, not the piping designer!