In practical situation, it is likely that they are extremely close to each other. In the OP situation, it asks for the electric cost which is the incoming energy to the house. It is possible that the electric energy go out from other wires such as the Internet wire.
And perhaps somebody is steaing your water! Watch out!
Electricity cost is calculated on wattage used as work (eg. producing heat), not current flow. The same current flows through your light bulbs, but doesn't cost as much since you
use less of it as work.