Today, I want to discuss underground water. We wouldn"t like to take out more than naturally comes into it. The 1 is that if you only take as much out as comes in, you"re not going to 2 the amount of water that stores 3 there. Right Wrong. That"s the 4 called safe yield. We can 5 as much water out as naturally flows back in. And the recharge 6 doesn"t change. So the 7 is we"ve reduced the amount of water that stores in the underground system. If you keep doing that long, if you 8 as much water out as naturally comes in, 9 the underground water level will 10 . In the underground systems there are natural discharge points. Well, a drop of water 11 can mean those discharge points will 12 dry up. Sustainability and safe yield are 13 , because what sustainability means is that it"s sustainable for all systems that 14 on the water, for the people who use it, and for 15 water to the 16 , like some streams. So, if we are using a safe yield 17 , we"re only 18 what we take out with what gets recharged, but don"t forget water also flows out. Then the underground amount gradually gets reduced and that is going to lead to another problem, the 19 and streams are going to 20 up.