The thing your asking can have consiquenses. You see there is single phase 220v and three phase. You probably have single phase at least it sounds like it as you can also see the plug looks different. Since your over seas you can also be dealing with 50 hertz instead of 60 hz like here in the US. If you use a step up transformer since its 220VAC if you plug into a 50 hz line it might cause a smoking of your power washer. Also with 220VAC you need proper phasing if you measure 220 single phase if installed correctly it has two 115vac lines which you wont get just taking normal taps off a regular step up transformer you probably will need an auto transformer so you can have three leads.That said consider the current draw which I assume will be in the 10 amp range that will tell you the wire size you need probably 10 ga to be safe with the correct plug you can do it. I forget what we used but are you supplying this from yellow gear or not if so use american parts if not well you better have proper circuit protection as well as isolation. So consult with an electrician who has been doing this for a while You will probably end up with smoke checked gear if you don’t . Do you see how complicated the issues your dealing with can be its not just plug and play my friend. Best advice be safe and since your in Spain check all safety devices as well as let an electrician do the wiring even if your just helping Electricity used correctly can be your friend but make a mistake and you could pay with your life. DO YOUR RESEARCH and SAFETY COMES FIRST. There s someone waiting for you to come home safely.