Mayoral candidate Rana Bokhari promises to spend more money replacing combined sewers in Winnipeg. Bokhari pledged Monday to increase annual spending on replacing combined sewers with dedicated pipes for sewage and stormwater from $45 million every year to $60 million. Combined sewers, which lie below older parts of Winnipeg, carry both runoff from the surface and sewage from homes and businesses. This mixture is pumped to one of the city's three wastewater treatment plants. When heavy rains exceed the capacity of city pumps, rainwater-diluted sewage overflows into the city's rivers. That, in turn, results in more nutrients — primarily phosphorus and nitrogen — flowing through Red River into Lake Winnipeg, where they promote the growth of algae and alter the ecology of the lake.