According to my wife, each year between say November to February our water
usage goes up about 20%. We live in southern Ontario.

She says it's caused by the humidifier on our furnace. I highly doubt that.
It is the drip type, not the drum type. Each fall I check to make sure the
water flow is adequate to moisten the panel, without spilling a lot into the
overflow. I also make sure it the water only flows when it should: fan
running and humistat switched on. We don't run the fan manually.

As for the water consumption, I think it probably has to do with wearing
heavier clothing which would lead to more laundry loads.

Any thoughts?

Marc