Like a lot of boat owners I have an electric bilge pump with an automatic float switch lurking in the depths of the bilge, to insure against accidental sinking when the boat is unattended. Coupled to two deep cycle golf cart batteries, which are connected to two solar panels, that little pump should keep working until the cows come home.
However, I often feel concern over the fact that if my fuel tank leaks and floods the bilge with Diesel the float switch will come on and merrily pump 33 liters of fuel overboard into the marina. Having seen what a cupful of fuel does in the water, I shudder to think of a whole tank full!
A little research turned up a float switch that is operated by having two electrodes that complete a circuit when immersed in a conductive solution (salt water) but will not activate when submerged in Diesel oil. Water Witch is one of these. I like the way it straps right to the pump, as shown in the picture below.
The one downside I see is that pure rainwater (does such a thing exist?) will not activate the contacts. But as I have a conventional stuffing box and there is always a dram of salt water in the bilge I don't see this as a problem.
I think this would be a worthy upgrade ... one of those little things you never see or think about while on the boat, yet providing peace of mind when the boat is unattended. Needless to say, before I make a final purchase, the usual research will be done to make sure this product is a "best choice" for my application.
I have installed this switch and it works well .... very simple and effective. Contrary to some reports it does respond to fresh water as well as salt water.