I'm trying to implement a water pipe inspection system using arduino but I don't know exactly how to use sensors to detect the leak. Most projects consider the valve is turn on, hence there will be a pressure or acoustic change on it, but for my project the valve is turn off so I'm thinking these methods can't be applied and a camera isn't the best option for now. Does anyone has any idea of how this inspection could work or how normally it's realized in water distribution network?
As you are already aware that the simplest method of leak detection of a pressurised system is by acoustics, it should be no surprise that the detection of leaks in a non-pressurised system can only be achieved by NDT (non-destructive testing) of the pipe carrying the water.
There are no NDT methods that can be implemented with an Arduino without considerable cost. If you've got loads of money to throw at this project, an Arduino wouldn't be the best starting point.