For many utilities, up to two thirds of the treated wastewater is infiltration water or inflow from combined sewers. This significantly increases operating costs but also capital expenditures as unnecessary investments in new treatment capacity has to be added. Another problem besides treating too much wastewater is that large quantities of sand and other particles can enter the pipes. This wears them down, decades before their service-life is expected to end.
Further, large quantities of untreated wastewater is released into the nature, where utilities are often unaware of the extent of the problem and where to focus their resources to reduce the problem.