Steam downloads and different user accounts.

Hi. I use a couple of different user accounts on my new iMac Downloaded Steam and Civ V on one user. Went to different user account and signed in to Steam to play Civ from that account. It wants to now download Civ again. As this took several hours, I really don't want to do this. Is there any way to be able to reference the single download as I am playing both from the same Steam account? Thanks.