Ive started walking the South Downs this year. There is Devils Dkye on the way, which has a pub on the top of the hill (might be happy to get you tap water). It is correct, a lot of villages of "off the downs", and it is a short sharp walk back up. There is also a NT camp ground just down the hill from DD, crossing over the main road (can't remember the name of it off the top of my head)