Dear Harnam,

Sorry if I ended up confusing you. Actually most of the time, people post very briefly without giving a background of the application or what exactly they plan to do. And end up getting replies totally out of focus.

Well since you appear to be new to this MCU stuff, suggest spend (plenty of) time in printing out the tutorials on the left of this page and go through them. Once you start getting a hang of it then you can start with your pump problem. In fact it will be a simple and nice one to learn I/0.

And in the meanwhile to do this ,

"Detect the low water level
Start the Water Pump
Detect the High level
Stop the water Pump"

You simply will have to use a level switch with 2 set points and use the signals to drive the power relay of the pump motor. OK just joking - sure you are doing this day in day out...

Raghu