It's easy to imagine a scenario where it might be necessary to provide one's own filtered water. Should that set of extreme circumstances ensue - or perhaps on a camping trip - here are some ideas that should see you through:

Homemade Emergency Water Filter Kit by IntenseAngler

Home Made Water Filter by Colhane

How to Drink Dirty Water in Emergency Situation - Survival !! by HadronMesons - Science and Tech

How To Make A Water Filter With a Bottle by THE DAILY PREP

Homemade Gravity Fed Water Filter by sunfloweroutdoor

Homemade Water Filter Setup by NCHiker1970