Slow sand filters absolutely work if you build them right and have patience. I set up a simple barrel system years ago with gravel, fine sand, and a layer of activated charcoal made from hardwood. The trick is letting that “biolayer” establish—it takes a couple weeks, but after that, the filter handles a surprising amount of water every day. Just have to clean out the top inch of sand every so often if flow slows down, but otherwise it’s low maintenance. Definitely not as quick as boiling for a batch, but it’s much less labor overall.
As for boiling, I’ve used a big canning pot outdoors on a wood stove for emergencies. You have to factor in fuel, especially if you’re talking long-term. Boiling’s reliable, but hauling all that wood
