What? Electrolysis? You mean electrolytic corrosion? No way, it always happen. You should use some good metal rods for this, like chrome-vanadium. like scrap screwdrivers. And low sense voltage, wich is amplified for desired level for your application. And i don't see any measuring circuit, that circuit is just a base for some audio peak detectors. This might be something like you are looking for, for detector i mean? http://www.electronics-lab.com/projects/sensors/027/index.html There's an idea of water level detector, uses DC and no worry of corroding because of VERY low voltage and when using durable metal rods.