The water level of an overhead tank can be controlled automatically by using parallel port of personal computer(PC) and required hardware circuit. A positional transducer is used to convert the water level of the tank into an electrical signal. This analog signal is converted into digital number which indicates various level of water in the tank by using an ADC. The output of the ADC is then fed to the parallel port of PC which make decision depending upon its input is that either the motors connected to the water pumps of the tank are in running condition or in rest, or which motor in the operation and which are in rest, and simultaneously displays the water level on its screen. The output of the parallel port is fed to the driver and relay circuit which are switched according to the water level.