A reed switch or other pulse sensor would work fine, and if microcontrollers are not an option a 555 monostable can be used as a "pulse is good" detector.

What pulse would we be measuring here???

 

I worked with water in my career and I can assert that the only (reliable for all circumstances) method of detecting the presence of or lack of water is by measuring the weight of the vessel that holds the water, ie, a weight control switch. These devices are commercially available or one may design his own. Any other apparatus that is used to detect the presence of water is subject to error or contamination or freezing or all of the above.
Cheers, DPW [Everything has limitations...and I hate limitations.]

 

What pulse would we be measuring here???

A pulse from a sensor, measuring the up/down reciprocating movement of the bore pump.