The most common and most likely answer to this crossword clue is the 7 letter word DITCHES
I've seen this crossword clue in The Daily Telegraph
D
I
T
C
H
E
S
More clues leading to the result DITCHES
Buddy explains!

The straight part
We know that "Watercourses/deserts" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case watercourses/deserts = ditches.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 DITCHES mean?
DITCHES noun- Dirt ingrained on the hands, or in cracks, crevices, etc.
- To smear, daub, plaster, or impregnate, especially with dirt which becomes hard and ingrained.
- A trench; a long, shallow indentation, as for irrigation or drainage.
- To discard or abandon.
- To deliberately crash-land an airplane on water.
- To deliberately not attend classes; to play hookey.
- To dig ditches.
- To dig ditches around.
- To throw into a ditch.