This data set reports natural abundance water stable isotope values (deuterium and oxygen-18) from the Marcell Experimental Forest (MEF) in Itasca County, Minnesota. Samples of precipitation, snowpack, stream, bog, lagg, soil water, upland runoff, lake water and aquifer groundwater have been collected since 2008 for chemistry measurement. Sampling is ongoing. The samples originate from multiple research plots and catchments, with many of the samples collected as part of the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment. Water isotopes have been measured for some but not all samples. More values from more sites will be added as the archive of water samples is analyzed for water isotopes. The MEF is operated, maintained, and funded by the USDA Forest Service, Northern Research Station. The SPRUCE experiment is a multi-year cooperative project among scientists of the Oak Ridge National Laboratory operated by UT-Battelle, LLC and the USDA Forest Service, Northern Research Station, with funding from the US Department of Energy, Biological and Environmental Research Program