* Sssshhh (like a hissing sound)
* Pshhhht (like a short burst of air)
* Tch-tch-tch (like a rapid clicking sound)
* Whir (if it's a rotating sprinkler)
* Sploosh (for a water fountain effect)
Ultimately, the best way to represent the sound is to use onomatopoeia - words that imitate the sound they represent.