I wouldn't think backpacking water filters would help much in for getting water from rivers / ponds in an urban/suburban environment? They'd take care of particulate matter and microbes but I doubt they'd do much for chemical contaminants.
Also, most filters can filter bacteria and cysts, but can't filter out viruses. Many say viruses are not an issue in the backcountry (but I still use purifying tablets), but if you're taking water from a suburban stream during a disaster, I'd definitely want to make sure I'm not ingesting whatever viruses the guy upstream deposited when he used the stream as a toilet.
