I'd base it on a hall effect current sensor such as the ACS712
https://www.digikey.com/product-detail/en/ACS712ELCTR-05B-T/620-1189-2-ND/1284593
You will also need a 5V regulator. To ave power this should be a switching regulator. Sparkfun, Digikey and even ebay have such regulators that will accept a wide range DC voltage and create 5V. e.g. **broken link removed**
Now you could do two things. I'd then use a voltage reference, buffer it and divide it and possibly buffer again to get the testing and pumping thresholds.
This info could be applied to a 3 wire bipolar LED or two lights.
Pumping water would basically turn out to be the color yellow for the easiest circuit.
Green (Preferred) or RED could be Checking for water.
You would have to play some games to get the colors RED for pumping and Green for ON and Yellow for checking or any combination of two or three colors (RED, GREEN, YELLOW) Red is one LED, Green is the other, Yellow is both on
It's nonetheless possible. Using Yellow for ON consumes power.
I just don't have the time to do a design. alec (not his handle) on this forum likes to do designs.
What would happen is that you would have two thresholds.
Checking
Pumping
For pumping I will be greater than the pumping threshold and the checking threshold.
For checking, it will be above the checking threshold.
Some LOGIC can probably create 2 signals from 3 inputs (power on, over checking threshold, over pumping and checking threshold) and create 2 outputs to drive, Green and Red.
A very simple way of doing the logic is to use two 3-input dataselector IC.
Not a real easy project, but very straightforward. I'll PM alec.