We live on top of the Cascadia Fault, so it is just a matter of time until The Big One hits. In case the odds are not in our favour we have a few different earthquake kits, which include water purification tablets.
In the event of a real big one it may be a long time before there is running water again, and so we bought a set of Berkey water filter elements.1 I actually bought these seven years ago, and was just relying on being able to find buckets and use a pocketknife to build a filter system if disaster strikes.
Source two buckets, ideally of the same size and style.
Drill a hole near the bottom of one bucket, sized for the spigot shank. Step drills are an underappreciated tool that are excellent for safely drilling thin stock, including sheet metal. The downside, though, is that they can quickly make a hole too large.
Put the lid on that bucket, then stack another bucket on top.
Drill a hole or two through both the bucket and the lid below it, sized for the filter shank.
Nest the buckets, pack the filter in lots of newspaper or bubble wrap, snap a lid on, then duct tape the other lid on, and tape the two buckets together so you can carry them by one handle.
I also packed a surplus square of polyester sheer fabric in the kit, which was leftover from our cider press. This is useful for pre-filtering water to take out leaves or other debris.
Now store your kit somewhere accessible in case of disaster. In an earthquake our old house will probably fall down, so the kit is in a garden shed.