Every time I brake hard the E-brake light comes on.

mine just started doing that too with 37k miles...I think I may just swap pads and brakes at the same time. How ofter should we flush the fluid?
 
I'm going to thread hi-jack here. My cars parking brake light is almost always on, the only time its not on is when I am shifting from first to second and if I am kind of on it from second to third it will sometimes shut off also but after I shift it will immeditately come back on. Anybody have any idea?
 
Is it your (!) E-Brake light or your Brake light that is coming on? Your ebrake uses no fluid so if the (!) light is coming on its b/c your car thinks the ebrake is ingaged. But if it is your brake light then it is very possible the answers above are right.
 
The E-brake light and the Brake warning light are the same thing.

The light comes on if your E-brake is up and your fluid level is low.

Never add fluid. Fluid doesn't evaporate, it either leaks or the level drops due to wearing pads. The light is sort of a safety as it warns you if the level drops because your caliper pistons will be extended to the point where you need to do a brake job. It's cheaper to just replace pads than it is to replace rotors too when your pads start gouging them.

If you add fluid it will spill all over your engine bay when you push the pistons in.

If your fluid level is low for other reasons...you have a leak