I live in Canada and if that water isn't heated before coming in contact with my hiney I can assure you that it'll be too cold for comfort at least in the winter.
I'm just back from holiday in Japan. All the toilets I used had heated (tepid) water. To me that's what made the difference between pleasant and what could have been awful.
It doesn't make much difference whether it's winter or summer. The water temperature isn't below zero or it would be ice. If the water source doesn't go below zero when the air temperature is -30, it's not going to get much warmer when the air temperature is +30.
