Start using salt water rather than fresh water for sewage systems.
Instead of flushing with fresh water we could be retrofitting and designing sewage systems to utilize brackish water. 30% of the world’s population lives near coastlines and everywhere we flush our most precious commodity, fresh water, down the toilet. Making this change to the City’s public washroom facilities, for instance, would make Vancouver a truly innovative, leading city. Salt water sewage treatment has now been recently been studied and successfully engineered at the Centre for Maximum Potential Building Systems in Texas, so it can be done.
Salt water is very corrosive and would cause piping to deteriorate very quickly. Plans are underway to allow the use of non-potable freshwater for flushing more easily.
Juvarya Warsi commented
Or perhaps even recycled greywater or captured rainwater?
would that not cause the metal pipes to rust? Think of the difference between Vancouver cars (mint!) and Ontario cars (rusty crudboxes!). This is from the use of salt on the roads to melt the snow. Would that not happen with the pipes? I think it's a great idea, but it might be a lot to take on if we have to replace all the old pipes in the city.