Impermeable
"Rock or soil that does not permit water to move through it perceptibly under the pressure ordinarily found in subsurface water." (United Nations Publications, 2013)
Sources
United Nations Publications. "Glossary of Shared Water Resources (English-Arabic): Technical, Socioeconomic and Legal Terminology." (2013). DOI:https://dx.doi.org/10.18356/70b462ce-en