No place even resembles the water flows of an urban area. We have straight, fast predictable flows over hard surfaces and through pipes. Streams are channelized, even disappearing into pipes and “magically” reappearing. Rain brings down the rich chemical mix arcing over us. Stormwater quickly washes the city clean, carrying away dust from streets and sidewalks and an even richer cornucopia of chemicals from buildings and other surfaces. A water-supply pipe squirts a small addition of hyper-clean water (except for chlorine, fluorine, and other chemicals) into the system. Another pipe or ditch system carries off and partially cleans the eternal concentration of human wastes so they don’t build up in the city. River water bulging with sediment and countless pollutants often squeezes through a city, sometimes with roaring floods, which clean out the accumulated toxics from industrial sites and carry off inappropriately located urban structures.

In contrast, out in natural land water generally flows more slowly, less predictably, and in crooked routes full of objects creating friction. The chemical mix washed down by rain and carried over surfaces is typically rather depauperate, often dominated by inorganic macro-nutrients. No pipe squirts in hyper-clean water, and no pipes carry off tubfuls of human wastewater. Clear water fills most rivers, while streams appear curvy, heterogeneous, often nutrient-poor, and seem to flow unendingly.