The most common and most likely answer to this crossword clue is the 10 letter word STANDPIPES
I've seen this crossword clue in The Daily Telegraph
S
T
A
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P
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More clues leading to the result STANDPIPES
Buddy explains!

The straight part
We know that "sources of water!" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sources of water! = standpipes.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 STANDPIPES mean?
STANDPIPES noun- A vertical pipe into which water is pumped so that a desired pressure is available at the bottom.
- The water supply of a building for the use of firefighters.