Laboratory determination of water retention curves for geosynthetic clay liners (GCLs) and their bentonite components are time-consuming, especially for high suction ranges. This paper explores the potential use of neutron spectroscopy as a useful method to assess the water retention properties of montmorillonite at suction levels >10 MPa for GCL studies. The results from neutron spectroscopy are in good agreement with traditional methods when assessing the water retention of bentonite and GCLs. Additionally, the primary advantage of neutron scattering is that, contrary to conventional methods, water populations within the clay matrix, such as bulk-like water, confined water, and structure OH, are observed and can be quantified independently.