Many investigators have conducted research on bioretention systems both in the laboratory and field. There is little consensus on which sources of water are best suited to hydrologically compact bioretention columns. Water with low ionic strength can leach ions from soil media, resulting in a different soil chemistry environment than would be found in typical bioretention applications. Soil columns were hydrologically compacted with three different water sources often used in column studies: deionized water, tap water, and rain water. Influent and effluent samples for each water source were measured for pH, conductivity, copper, zinc, and phosphate. On average, deionized water yielded larger percentage increases between influent and effluent for pH, conductivity, copper, and zinc, indicating that deionized water leaches out more ions from bioretention media than tap water or rain water. To maintain soil chemistry similar to the field, rain water or tap water should be used in column studies.