Camelbak has a new ultra violent treatment system and Sawyer has a tiny squeeze thru filter. I'll find the brand names for further research.

TeacherRO...if you are looking for only emergency water filters.. look at the Sawyer 5gal kits .1 micron and .02 micron... they don't have the inner activated charcoal stages that the Doulton or Berkey have, but don't need to be replaced..they can be backflushed.. I added a small PVC column of aquarium grade activated charcoal...check out the Adventure Safety Products... I think they are the internet outlet for Sawyer... a Doulton candle cartridge in a 5gal bucket on top of another 5 gal bucket is a lot cheaper than a Berkey

Ultra violent water treatment sounds interesting.
What sort of violence is employed ?
Does this violence endanger nearby persons or property ?
Perhaps only suited to remote locations, not urban ?

Sorry,could not resist

ok - Violet. Ultraviolet. there

Sawyer Squeeze™ Filter is one and the camelbak all clear is the other

Also looking at various versions of the steripen...

Hehehehe!