What is the quickest?
You want to double your bills? Seriously? To double your water bill you need to use a lot more water. Try leaving a few taps on all day. To double your electricity bill you need to use more electricity. Leave a space heater or two switched on and turn them up to maximum. If it gets too warm, open the windows to let the heat out (This works really well in the colder months; in the summer months try turning all the air conditioners to maximum and leaving some windows open to let the warm air in) Using a lot more gas is tricky without adding an element of danger, but perhaps you can turn a gas heater on maximum, maybe turn all your gas burners on high and leave them running for a few extra hours. Im not sure why anyone in their right mind would want to double their bills but you asked, so..