Bromate formation experiments were carried out in a 100 l/h bench-scale dissolved ozone plug flow reactor (DOPFR) with natural filtered water from the drinking water treatment plant Leiduin of Amsterdam Water Supply at gross ozone dosages of 0.7–3.4 mg/l. In the DOPFR, ozone is dosed by intensively mixing a dissolved ozone water flow (side stream) with a test water flow (mainstream). The side stream is pre-treated to remove bromide and DOC and to lower the pH. For full-scale application of the DOPFR concept, it is most cost effective to apply the smallest possible side stream. This research is done to establish the effect of decreasing the ratio of the dissolved ozone side stream to the mainstream from 1:10 to 1:25, by increasing the ozone concentration and decreasing the flow of the side stream. The results show that the dosing ratio has no influence on the bromate formation in the ozone dosing range of 0.7–1.4 mg/l. The gross ozone dosages that are currently applied at the drinking water treatment plant Leiduin are 0.8–1.0 mg/l. This means that for application of dissolved ozone dosing at Leiduin the amount of ozone that can be dissolved in the side stream will be the limiting factor for the minimal flow of the dissolved ozone side stream.