The most common and most likely answer to this crossword clue is the 8 letter word RACEWAYS
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Buddy explains!

The straight part
We know that "channel carrying water" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case channel carrying water = raceways.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does RACEWAYS mean?
RACEWAYS noun- A place where races are held; a racetrack.
- An easily-accessible conduit or tray for organizing runs of data or power cabling.
- The canal for the current that drives a water wheel.