How much water should I bring + any tips to get more?

Me and 3 of my mates are gonna be hiking for the first time, specifically the south downs trail (England) soon for 3 days (+2 nights). We’re most likely going to be wild camping and i’m curious to know how the veterans conserve and acquire water on trails, how they pack it, and if you’d like i’d also appreciate some wild camping advice and stuff like that.