In Florida, water is easy to come by...not necessarily potable, but it is everywhere. In the worst-case scenario, I can get sustenance water from sea water with solars stills. But I know a lot of you guys are out in the desert southwest where water is harder to come by. In a SHTF situation, if you find water in a muddy pond or a golf hazard, you shouldn't pass it up. But drinking that sludge is asking for disease, so here's instructions for an inexpensive DIY Berkey water filter setup.
Berkey water filters are stainless steel with capacities suitable for up to 40 or 50 people. The smallest ones run over 200 bucks. But what you need is the filter elements themselves
... screw the stainless steel... save a bunch of money and install Berkey elements in plastic buckets for less than $20.00. Prepare your buckets, stack them, put the elements inside, put the lid on it, and stick it in your garage, content in the knowledge that you have years of drinkable water available.
The elements are kinda expensive (about $90 a pair), but each one will filter 3,000 gallons. So, 2 elements= 6,000 gallons. Calculate 1 gallon per person per day, so 6,000 gallons / a family of 4 needing 1 gallon per day per person= 1500 days of water, or 4 years and 5 weeks of drinkable water.
So 4 elements would give your family of four 8 years of drinkable water from a nasty ditch for 200 bucks... in a SHTF situation, that sounds like a bargain.
These filters remove all sorts of germs, viruses, poisons, and other nasties. You should give pond water a "rough filter" through a cloth filter of some sort before going into your bucket, and you should wrap the Berkey filters in thick cloth to filter any large solids to help preserve your filters (they suggest cloth diapers in the how-to). They can be scrubbed with Scotchbrite pads to clean them up. I'd still probably use a drop or two of bleach per gallon.
DIY Berkey Water Filter