I have an adapter (whale I presume) so that when you’re on site you a plug your water system directly onto the tap if available. This device I had from a previous caravan a long time ago. The question is will the eriba water system usually take mains pressure or should I just keep to my aqua roll ?

If the device you mention is a pressure-reducing valve designed for the purpose then yes, in theory you can connect mains pressure to the van's water inlet.

But as you say, it's bobbing on a bit and I wouldn't trust the thing as the van's water connections, taps etc would spring leaks under mains pressure if the valve was faulty.

Best thing to use is an Aquaroll mains adaptor which ensures mains pressure is isolated from the van's water inlet.

That's what I bought last year to use with our "offboard" Aquaroll-based water system on our "old" Triton. I'll be installing a similar system in our "new" Troll at some point, as the two onboard water tanks are too small - and take up valuable cupboard space, as well as being fiddly to refill...

I too would be wary of plugging mains water directly into my caravan! Friends of mine had a plastic water pipe junction fail in their home bathroom - it was amazing how quickly the room below it became a swimming pool, and the waterfall down the stairs was something to see, apparently...