http://www.supportnow.biz/step-instant/

What do I need to power a 110v Instant Water Heater in Aus?
It’s detailed as 4kw and 110v – these are all the specs available to me.
Am I correct in thinking this will pull 4000w? (That’s huge!!).
Considering it will only be used for short showers by me a few times a week, can I get away with a less robust step down transformer?
you will need something that is rated at a minimum of 5000 watts. anything lower will over heat and cause a fire.