what is not how what works? What goes up must come down right? if you force it to come down in one place, it wont come down in another... Seems simple enough.
No, it is not that simple. Most moisture in the sky is dissipated not through rainfall, but through running into a dry air mass that then lowers the humidity enough to "dry up" the cloud and make it disappear. What ends up on the ground is only a fraction of the volume of water in the clouds above.
If it were as simple as you suggest, you have just developed a method for preventing floods. All you'd have to do is cloud seed to start draining the water out of the sky before it got to where Mother Nature would have originally wanted to put it.
But I digress and will let you all get back to your regularly scheduled programming.