The most common and most likely answer to this crossword clue is the 8 letter word HYDRANTS
I've seen this crossword clue in The Times
H
Y
D
R
A
N
T
S
More clues leading to the result HYDRANTS
Buddy explains!

The straight part
We know that "Water sources" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case water sources = hydrants.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 HYDRANTS mean?
HYDRANTS noun- An outlet from a liquid/fluid main often consisting of an upright pipe with a valve attached from which fluid (e.g. water or fuel) can be tapped.