Water filtering
Link dump
Small scale DIY
Charcoal/Sand/Gravel in a plastic drink bottle
https://waterfilterguru.com/how-to-make-a-homemade-water-filter/
Carbon and heated coil, 2 stage filter
https://www.youtube.com/watch?v=2fr5TjZK4ZQ
Permanent, for the home
5 stage system for the home, as an alternative to Reverse Osmosis
https://www.youtube.com/watch?v=WCC4TOYYGF8
Interesting permanent solution for the home involving two sediment filters (20 and 5 microns) followed by a carbon filter
https://www.best-osmosis-systems.com/diy-whole-house-water-filter/
Water purity
Good overview of what the various filtering systems remove, thus was level of purity can be expected