In more than 700 American cities, especially older cities east of the Mississippi, sewer water and storm water share infrastructure, which means that major weather events can all too easily lead to raw effluent escaping into waterways. With global warming creating more-frequent and less-predictable extreme weather events, more and more cities have to deal with this most unfortunate confluence. It should be a call to action both because it’s a serious problem and because individual efforts can combine to make a real difference in the health of our waterways and communities. The solutions are basic and straightforward: green roofs, rain catchment barrels, permeable pavers, storm water gardens, and bioswales. All these individual efforts help to slow and filter the flow of storm water so it doesn’t overwhelm the system. Done well, storm water can be filtered by plants and absorbed into the ground without ever reaching a treatment plant. Nate Griswold is an architect, the founder and president of Inhabitect, and an early proponent of green roofs who has installed more than a thousand systems. Griswold …