Interactions between surface irrigation water, river water, and shallow groundwater may have effects on water quality that are important for both drinking water supplies and the ecological function of rivers and floodplains. A study focusing on changes in concentrations of soluble ions in groundwater compared to surface water from an irrigation ditch and the Rio Grande was conducted in northern New Mexico. The objectives were to identify sources of shallow groundwater and how those sources relate to changes in groundwater quality during and after the irrigation season.