The most common and most likely answer to this crossword clue is the 4 letter word BONG
I've seen this crossword clue in Independent
B
O
N
G
Buddy explains!

The straight part
We know that "Water pipe" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case water pipe = bong.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 BONG mean?
BONG noun- The clang of a large bell.
- Doorbell chimes.
- To pull a bell.
- To ring a doorbell.
- A vessel, usually made of glass or ceramic and filled with water, used in smoking various substances; especially marijuana or pot.
- An act of smoking one serving of drugs from a bong.
- A device for rapidly consuming beer, usually consisting of a funnel or reservoir of beer and a length of tubing.
- A very wide piton.
- (thieves' cant) A purse.
- An Australian Aboriginal person.