interstitial water

synonym: pore water
https://doi.org/10.1351/goldbook.14772
Water in sediment or soil that surrounds the solid particles. The amount of interstitial water is calculated and expressed as the percentage ratio of the mass of water in the sediment to the mass of the wet sediment.
Source:
PAC, 2009, 81, 829. (Glossary of terms used in ecotoxicology (IUPAC Recommendations 2009)) on page 902 [Terms] [Paper]