groundwater

noun

1. (countable, uncountable)Water that exists beneath the earth's surface in underground streams and aquifers.

   “The pH in water of the hillside soils varied between 3.1 and 6.1 with a mean of 4.2. The pattern of pH variation is complex and does not clearly relate either to cultivation or occupation. The most consistent, though weak, correlation appears to be between higher pH and flushes or bogs, which indicates that the local groundwaters are comparatively basic.”

   “Research has shown bone apatite to undergo chemical exchange with carbonates in either vadose water or groundwater.”