Steripens (a water purifier, not filter) are great very portable but limited in capacity.
Katadyns are very good and portable but expensive and also limited in capacity.
Bleach has a limited shelf life. Pool shock (Calcium hypochlorite) has a long shelf life and can be used to make a solution for water purification.
Have you heard of the WAPI? It’s very low-tech, costs about $9 or so at www.sunoven.com. It’s a water pasteurization indicator. It won’t filter your water but will let you know when water (and milk) have reached the temperature for pasteurization.
Berkeys can filter thousands of gallons of water before the filter needs to be replaced. There are also directions on the internet for making your own ceramic filter.