Ok, there are three lines, yes? One for water input and two for water output. The output lines are for RO water and waste water. The RO water line is what you collect, the waste water line is what you let drain. Yes, while you are making RO water the waste water line will always be producing water. In fact, it should product about 4 to 5 times as much water as the RO water line. If you have the water turned off and are not making RO water, and your waste water line is still going, you've got a problem somewhere.