1998 GMC C2500 Leaks a small amount of water.

I have a slight coolant leak. It uses about quart a week. I have heard this is a common problem with this specific auto. We have a 97 chev Pkp that does the same thing also. You can always smell antifreeze
when you get out of the vehicle. But not enough to
find the leak. Have you heard of the cause of this?
Thank You Art Bohr