A pilot multi-stage filtration system for water treatment was operated at two sites with phosphorous nutrient limited and nutrient rich source waters. The system had two parallel treatment trains: Train 1 consisted of pre-ozonation, roughing filtration and slow sand filtration (SSF); and Train 2 consisted of pre-ozonation, roughing filtration and biofiltration (BF). Nutrient limited conditions exhibited lower DOC removals than nutrient rich conditions when ozone was present (9.3% vs 26% DOC removal, respectively). However, there was no difference in removal when no ozone was present (5.6% vs 6.4% DOC removal, respectively). At the nutrient limited site, there was no overall difference between removals in the SSF and BF under conditions with and without ozone (p>0.05). At the nutrient rich site applied ozone resulted in a difference in removal between the SSF and BF trains (p<0.05), while there was no difference between the trains when no ozone was present (p>0.05).