The study presented in this paper deals with the computation of the in
creased hydraulic loading of the treatment plants in the Greater Copen
hagen area due to the installation of more storage capacity in the com
bined sewer system in the future. A mathematical model is set up for t
he entire sewer catchment and predictions of future increased hydrauli
c loadings are made for various development scenarios. The computed in
flow conditions are presented on a statistical form. The results show
a significant increase in the hydraulic loading of the plants due to i
ncreased storage volume in the sewer system. The computed inflow stati
stics are used in the design of the treatment plants to ensure proper
plant performance during prolonged periods with full hydraulic loading
due to storm water.