[Cthulhu_]

You'd think most countries would have good drainage by now, which includes filtering and reusing as much rain water as possible before dumping it back into the rivers / oceans / etc. I know in most towns over here, rain water goes through a different sewage system than sewage and isn't just discarded in the nearest river.

[code_duck]

Much infrastructure in the US is old and critically underfunded for maintenance, much less improvements, even when inadequate. Witness the drama over the collapsing Oroville dam in California, the collapsed bridge in Minneapolis, or more specifically, sewage overflows in Great Lake states.

I lived in Duluth, MN, and anytime there was significant rainfall, the sanitary sewer system would be overflowed by storm water, and dump thousands of gallons of untreated sewage directly into Lake Superior. http://www.duluthnewstribune.com/news/3772570-court-order-du...

It is a problem for the whole region: https://greatlakes.org/campaigns/sewage-overflows/

[Steve44]

It's to do with how fine these plastic particles are and the sheer volumes of waste which need filtering. They do remove a fair percentage but not all. [1]

Even in regular drains there will be a significant amount of contamination which would prevent the water from being used as-is; if you have a specific rainwater collection system that would work but is basically what our reservoirs are now.

[1] https://www.patagonia.com/blog//2017/02/an-update-on-microfi... "wastewater treatment plants filter a good amount of microfibers (65–92 percent) but still release a significant volume of waste into the environment"