What is purified water? You need something to sterilize the water. Some filters can take out the dangerous pathogens but chemicals like the EPA’s Colorado spill had heavy metals also.
They make filters that do both. Evey on seems to think that you will just need to boil water, but there will be all kinds of chemicals and runoff that boiling it just won’t do the job.
You need something like a Berkey especially if you are needing water for more than one or two people.