ABSTRACT
In general, techniques extending the physical range of water recovery appear to be more in the domain of the future than a part of the past and the present. They accordingly make up an important part of the discussion in Part III (chapters 13, 14, and 15). Nonetheless the past offers some illustrations of the meaning of extending the physical range of water recovery. Extension of man's capacity to exploit water may be made within the tropospheric part of the atmosphere, into geographical environments hitherto unavailable for exploitation (like the oceans), or into the rock formations underlying the surface of the land. The illustrations here selected are principally from the latter field, that of ground-water exploitation. One additional case is an extension into the new geographical environment of hitherto unusable surface waters.
