Storm water management. When you have buildings, the rain water does not get soaked up by the concrete (unlike lawn) and it goes to the storm drains. This has to be maintained. This is already part of the water rate. Newer part of city has storm drains hooked up directly to the rivers and lakes. Older part still goes to sewer and that gets treated at water treatment plants.
It is not a new charge, just the calculation is changing. Kevin Voung is the guy that coined the term rain tax.
This was proposed during Tory's term as mayor. It is just getting tabled to go into effect now.
National post link, unless it is not right wing enough for you.
The stormwater charge (to give it its proper name) would mostly reduce water bills for apartment and condo buildings
nationalpost.com