Trigger on power loss latch system

I'm trying to create an auto filling water reservoir. I want to create a container that knows when it empty and knows when it is full. So the thought was, there would be 2 sets of contacts; one set at the base of the container and one at the top of the container. I'm wanting to feed the negative side through the water. When the water drops below the bottom set of contacts it should trigger the valve. Then when the water gets to the top set of contacts and connects them, the valve should be shut off. The top contacts losing power shouldn't do nothing. And the bottom contacts regaining power as the water fills should do nothing. So, basically, bottom set losing contact is on and top set gaining contact is off. I thought a latch system that feeds negative instead of positive might work. It doesn't. I've found two problems. I'm not sure how to trigger the latch on power loss (bottom contacts). Also, since the water will be connecting the bottom contacts as the water is filling, the top contacts wont actually break the latch because the bottom contacts will still have a constant negative feed. I know this is kind of confusing. I'm pretty good with electronics, but I'm kind of hitting a wall on this. Any help is greatly appreciated.