We catch our own rainwater when we are camped up somewhere in inclement weather.
Just slightly tilt the awning, hang a funel and a hose with a container (in our case one of those plastic tug thingys) on the lower end and then filter it into your jerry can.
I also carry a Brita water filter jug. I change the filter every month. As I rely on mains water these days, it's a good way to ensure the water tastes the best and any impurities are removed. Adelaide used to have the worst water in Australia. Even ships wouldn't fill up here, but these days it's filtered much better and purified to a high standard. Water availability is more of an issue outback in places which depend on bore water and rain water. It always pays to ask the locals. Cheers!
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20ft Roma caravan - Mercedes Benz Sprinter - SA-based at the moment. Transport has no borders.
Management makes the decisions, but is not affected by the decisions it makes.
I rarely buy water (a recent exception was in China where everone advises not to even clean teeth with tap water even though it looks good. Fortunately the Hotels always provided two complimentary bottles daily & a boiled jug overnight provided extra).
When caravanning I have an Instapure filter on the tap that I replace according to instructions. I just use whatever water is available or out of the tanks.
As a reserve I have an old plastic 20L container, but where I feel that more is required I fill up several 4L washed wine casks (have a steady resupply of those) & carry them in a milk crate or as packing in the Engel.