In addition to the previous post and suggestion, get yourself a little box and keep a range. Most site taps need a screw-on adaptor which can come in two sizes. A trip to Bleedin Q or similar stores will have a range in the gardening section. The Europeans have all sorts of taps! These range from bog-standard domestic types - where you can use the connector pictured in the above post - to those with screw on terminations.
It's not just a question of the adaptors either. It depends upon how far you are away from the tap! If you aren't on a 'posh' site where the pitch has its own service points, fill up with water when you enter the site. The reception staff will tell you where the water points are. (Fresh water is called Eau Potable in French). I always take a 5 litre canister (purchased from Icelands store) then re-fill it after that arrival cuppa. Or, get a larger plastic food grade 'Jerrycan' to save getting the filler hose out and moving the 'van.
I don't think there is a universal fitting for all taps .... I carry a box with around 15 different connecters and have used most them at some point .... I have also still been caught out without the correct one at times
P's. I am coming across more now that require a male Hozelock type end to push into a female outlet that start gushing as soon as you push it in.