As the world population increases, the demand increases for quality drinking water. The harvesting of rainwater has the potential to assist in alleviating pressures on current water supplies and storm water drainage systems. Diversion of a portion of the collected water away from storage is a technique used to improve harvested rainwater water quality prior to storage. Six configurations of a downspout first flush diverter were constructed and tested in the laboratory. The configurations of diverters were evaluated for their affinity to allow diverted water in the diverter chamber to interact with the flow of water to storage. Experiments were conducted at flow rates ranging from 0.76 L/min to 113.56 L/min. This range of flow rates adequately represents a wide range of common storm intensity patterns across the United States to which downspout first flush diverters are subjected. The diverter chamber to downspout transition fittings tested on a 10.16 cm diameter diverter chamber, upward and downward oriented sanitary and straight tee, do not have a significant impact on the mean difference in initial and final total dissolved solids concentrations observed at multiple sample ports. No statistical difference was observed when comparing upward and downward oriented sanitary tees used as diverter chambers to downspout transition fittings on 10.16 and 15.24 cm diverter chambers. Utilizing a straight tee as a transition fitting with a floating ball, acting as a barrier between water collected in the diverter chamber of a downspout first flush diverter and the flow passing through the transition fitting, limited diverted water from interacting with the subsequent flow of harvested rainwater. There is not a significant difference between the use of a downspout first flush diverter with diverter chamber diameters of 10.16 and 15.24 cm utilizing upward and downward oriented sanitary tees as downspout to diverter chamber transition fittings. Tests at flow rates less than or equal to 12.11 L/min exhibited limited changes in total dissolved solids concentrations in the downspout first flush diverters with 15.24 cm diameter diverter chambers. Tests at flow rates less than or equal to 1.51 L/min exhibited limited changes in total dissolved solids concentrations in the downspout first flush diverters with 10.16 cm diameter diverter chambers. The diverter chamber drain flow rate and volume impacts the observed differences in initial and final TDS concentrations at all sample ports on the diverter chamber of a downspout first flush diverter regardless of flow rate. The diverter chamber drain flow rate impacts the flow rate of water entering the diverter chamber through the transition fitting.