By depriving a camper of water (3)
I believe the answer is:
Here is my best explanation:
'by' is the definition.
'depriving a camper of water' is the subsidiary indication.
'per' is hidden in amongst the letters.
However, I'm unsure how the hidden word is indicated.
(Other definitions for per that I've seen before include "Through", "Preposition indicating by means of", "For each or by means of", "According to", "Preposition meaning for each", "For each or every", "By means of" and "A".)