Sup gurl. What is exactly leaking. 

Normaly when you hit the underbelly of a car what gets hit is the oil pan. If what is leaking is the oil then you may have to take the car for a diagnosis, dont let them fool you a leak can be welded they dont need to replace the part.

If it's pure, clear-looking water, and not oily, and if it only "leaks" right after you drive it with the a/c on and not at other times, then it's just the a/c. In that case you have no problem.

If it's bright green, then it's anti-freeze and you rather do have a problem, although I can't imagine what you might have scraped on the bottom of the car that would cause that sort of leak.

If it's reddish and somewhere between oily and sticky, then it's probably transmission or brake fluid, and you're going to have to have it looked at.

If it's mostly black and completely oily, then it's engine oil. That will need to be looked at too.

If its possible to check whether its leaking water (which is ok) or something else (which is not ok-check for smell and colour) than that's one way to diagnose. konadh324's word is also good.

The AC always leaks water. It's a good thing. When you say hit, as in like you were parking and it scraped or did you hit it with speed? If it's the former, then you're fine. Probably just the bottom of the bumper scraping.

Oh, and check all fluid levels while you're at it. Coolant, brake fluid, power steering fluid etc. Always good to be sure. And having fluids topped off is always good. Touching and smelling these fluids isn't dangerous either just so you know, to an extent at least, a quick whiff is fine. Coolant smells sweet, oil smells like, well, oil. Oil is black if old or goldish if new, coolant is green or red, power steering and transmission fluid red (usually) but much thicker than coolant. And brake fluid brownish yellow. Brake fluid will cause hands to prune very quickly if touched. So don't freak out if that happens. If all the fluids are good, and it goes down the road fine,  no real damage was done. With oil being low you will usually get a dummy light (check engine light). But always check to be sure.

Does it still drive okay? If you were to have torn a CV boot that would not be good. Also, look to see if the stuff leaking is just water (condensation from AC) or if its oil. If its oil that needs to be addressed ASAP. You will blow your motor up if you run it out of oil. Before your next drive check the dipstick level. If there's no reading. DO NOT start it or drive it. In the worst case scenario you cracked your oil pan. If the dipstick shows close to full, take it for a drive and see if anything is abnormal. You may need an alignment if it is pulling you to one side or the other. And there's a good chance you bent a rim, which will cause wear on many things over time. Mainly tires and suspension. And it will violently wobble at high speeds. If everything checks out, I wouldn't worry about it. People bash curbs all the time. I got air in my ford on one the other day haha. Usually they don't do much damage but I have seen curbs mess up cars pretty bad. Best of luck!

Could possibly be anti freeze. What color is the leakage? 
Your coolant may need to be replaced/patched.  
If that's it then be careful. You over heat the car and fry the engine.