Correct Answer - Option 3 : Detecting of leakage in underground water mains
Explanation:
The following methods may be used for detcting the lekage of water from the under ground water mains
(i) By direct observations
(ii) By using sounding rod: Stethoscope type instrument is used, also called aquaphone or a sonoscope
(iii) By plotting hydraulic gradient line
(iv) By using waste detecting meters
