Circuits for water level indicators have been fairly common in the market. Most of these suffer one sort of drawback or another, perhaps the most serious being the corrosion of metal electrodes due to the electrolytic reaction between minerals dissolved in the water and sensors. That is why roof-top water tanks warrant more frequent acrobatics from the user of the conventional devices. Here is a collection of water level indicator circuit with minimized electrolysis.Water level indicator circuit using bipolar junction transistor, silicon controlled rectifier, timer ic555, hex inverter gate icCD4049 are the few to mention. All the circuits in this website which operates in AC/DC power supply uses alternative signal as input.