A low power and simple circuit for capacitive level sensor has been described as follow:

https://www.best-microcontroller-projects.com/capacitive-liquid-level-sensor.html

If the specification is about 10 µW, the "trick" is to have the sensor switched off ("sleeping") for most of the time, rarely waking up, assessing the current level and going to sleep again.

The measurement principle is of little relevance, provided the setup is of high resistance. The easiest of all would be to measure the rise and/or fall time of the RC low-pass consisting of a series resistor and the capacitance of your sensor. This one takes some time, but will work even with a microcontroller at lowest clock rates.

Microchip (Microchip + former Atmel - https://www.microchip.com ) have a numer of microcontrollers (look for "nanoPower" and similar designations) that might fit you requirements.

Mr U. Dreher What I understand from you point is measuring the charge and discharge time of my capacitor(sensor) but how would I be able to measure it. What will be the components of my circuit.

Thank you so much.

Attached you will find a rather mature document handling - among a lot of other topics - how to measure RC rise/fall times. Although written for a certain microcontroller family, the principles shown are applicable to virtually any microcontroller.

My hope is this will give you a kickstart to dig deeper into this matter.

Mr U. Dreher and Mohammad Soroosh the problem with building a simple RC sensor is the on and of time and measurement cycles . what If the water is of mm liters. In my use case we have water which is leaking through walls, is needed to be detected, there is a small canal where water will finally end up and thats the point where i want to place the sensor or the prototype .

Any other ideas that you could give on building such a sensor and ofcourse with maximum of 10 micro watts of power.

Thank you

Hello,

die amount of water doesn't really matter with respect to capacitance changes. It's just the electrode ("capacitor plate) design that has to be adapted.

(You may not know about that, but capacitive touchscreens are basically affected by raindrops. "Nullifiying" this effect is not trivial although doable. So it is not a matter of the measurement method (RC timing measurement is really OK), but some matter of sufficent measurement resolution and clever electrode design.

Provided your "small canal" is really a canal (water flowing), an electrode at the bottom might do. If it's more like a pond (water accumulating), a vertical electrode with sufficient area might be what you need.