Rural Water Supply Sensor

I am a complete newbie and I want to build a water sensor to be used in rural water projects in Africa. What I would like to achieve is to have the water sensor on the pipe coming from the overhead water tank and supplying the taps, this way I will be able to tell if the villagers have been getting water from the tank. If the pipe is dry for up to 24hrs I would like to receive an SMS alerting me that the taps are dry. Power supply to the kit should ideally come from a solar panel or from the power supply to the water pump. This is in addition to the onboard battery of course.

Thank you very much

Please check this recipe here.