We have already posted about a How to make a Water Level Indicator & Controller using micro. Today I am presenting a very useful, very cheap and very simple circuit using transistors for beginners in the field of electronics. This simple circuit can indicate the level of water in your tank using LEDs.
The connections and arrangements are made as shown in the figure above. The +9V is supplied to water using a metal contact. In this circuit all the transistors are working as a switch. When the water touches the metal contact in which base of each transistor is connected, a small current flows and turns on the transistor. When a transistor turns on, LED connected to it glows. Thus LEDs will be turned on depending up on the level of water. By using a relay we can also control the level of water.
Article courtesy of electrosome.com