1. To become dissolved, eroded, or carried out (of something), by or as if by some percolating liquid. Nutrients have continued leaching out of the soil as the groundwater become more acidic. As water levels rose above the layers of sandstone, calcium slowly leached out over time.
2. To dissolve, erode, or carry something out (of something else) due to percolation. In this usage, a noun or pronoun is used between "leach" and "out." Increasingly acidic water has been leaching important minerals out of the land. He said that, over time, the saltwater would leach out the calcium within the limestone.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.