Influence of equilibration time, soil texture, and saturation on the accuracy of porewater water isotope assays using the direct H2O(liquid)–H2O(vapor) equilibration method

•Direct liquid–vapor equilibration (DLVE) method is used to analyze δ18O and δ2H.•The efficiency of conventional Ziploc bags for isotopic equilibration is tested.•The effect of soil texture and porewater saturation using DLVE method are shown.•Soil sampling techniques influence the isotopic equilibration time.•The presence of organic matter in soil causes isotopic enrichment in Ziploc bags. The hydrogen and oxygen stable isotopes of water (δ2H and δ18O) are powerful tracers for studying subsurface water flow processes, but the extraction of porewater from unsaturated soil is complex and laborious. The direct liquid–vapor equilibration method (DLVE) for isotope analysis overcomes this challenge by analyzing headspace vapor in isotopic equilibrium with the porewater under closed system conditions. However, the effect of the equilibration time, soil texture, and porewater saturation on isotopic results is not fully understood yet. We tested three differently textured, disaggregated soils (sandy, silty loam and clay) to assess how the equilibration time is impacted by (i) porewater saturation (100%, 80%, 60%, and 40%), and (ii) soil surface area. For all tests, the water loss through diffusion was negligible (