Doubtless most of you are more familiar with surface reservoirs, their capabilities and limitations, than you are with ground-water reservoirs. I believe that this is true of people in general, even the experts. And because of our inadequate knowledge of ground-water reservoirs, our use of them creates problems that are rarely if ever encountered in the operation of surface reservoirs. Nevertheless there are many similarities between these two basic forms of water storage, and I should like to point out some of these similarities, was well as some important contrasts.