A supply or resource has been exhausted, as in There's no more principal left; the well's run dry, or There's not another novel in her; the well's run dry. This expression likens an underground water source to other plentiful sources. Benjamin Franklin used it in Poor Richard's Almanack (1757).
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.