How can I detect with arduino when separate alarm sensor detects water leak.

I have a simple water alarm sensor that runs off of 9V battery. It is very similar to this product.

Water alarm sensor

So basically the way Alarm sensor works is, it has 2 wires extending from it where one of the wires always carries about 9V. When the wire carrying 9V comes into contact with the other one, the alarm goes off. I was wondering if there is a way to detect this with Arduino. I tried connecting the 9V battery - to my arduino GND and then lowering the voltage to 3.3 volts and feeding it to an analog pin on Arduino, but it does not work.

Yes, it should be possible to detect this with Arduino. We cannot say why it did not work for you because you were much too vague when describing what you did. Post a schematic and your code. Read the "please read" post to find out how to post images and code.