In reply to monsoon:
We lived in our van for 2 months in North Wales last Summer and had a great time.
Parking: there's lots of free parking spots that are well used. We would move around every few days so as not to give the impression of setting up camp / taking the p**s. The Pass layby can be noisy but this is offset by waking up next to the climbing and the water supply is a hop over the wall in the stream. Toilets at Nant open 8am ish. Bus Stop Quarry turning is also a very popular van spot BUT be mindful, no easy access to toilets and (rightly so) locals are getting fed up with their back yards in essence being used as loos ------ The layby at the base of Tryfan also a good spot. The toilets at Ogwen were open 24 hours last Summer. Not quite so easy to get water.
Water: Llanberis Pass stream. Lake Padarn. It's up to you if you want to filter it etc.
Showers: Pete's? Other than that, not sure. I swam in lake Padarn most days which freshened me up no end
Have fun, spend money in local businesses, be respectful and don' look like you're setting up home and you'll have a fab time
Post edited at 07:42