Many have become exposed to the concept that water flows toward a stream, and then "downstream" from that point. Watersheds are the units in which these streams drain, i.e. a drop of water can hit at the top of a watershed, along a ridge, and flow toward a stream, within the watershed. Within watersheds, there can be forests, lakes, cities (or parts of), and all of these attributes affect the water quality within the watershed, as well as the water quality exiting the watershed. 
The image above illustrates the concept well. It is important to look at watersheds, at a local scale (subwatersheds) and at larger scales (regional watersheds, if you will) so as to understand where water quality inputs are affecting the system. Development can, and often does, negatively impact water quality in watersheds. Primarily, this is due to the installation of impervious surfaces over what had previously been pervious, or able to allow water to infiltrate. Thus, in developed areas, stormwaters "runoff" impervious surfaces much more quickly than in undeveloped areas, quickly trickling to the lower point of the watershed, and into stream and river systems, causing flash floods.
Citizens living "downstream" from these developed areas are often the ones who experience the effects of flash floods. They are outraged, as they have the right to be. However, the answer is not to create more engineering marvels along the banks of the stream to prevent floodwaters from reaching their floodplains. No. The answer is to treat the source of the problem. We can no longer build enormous amounts of impervious surfaces, such as substantial surface parking lots, and big-box stores, and ignore the negative effects of such elements.
Let's consider a situation. If we do continue to develop as we have, and flash flooding continues to increase in downstream areas, it requires spending millions of dollars not only to prevent further flooding to occur (which actually is bad, because it causes even more damage farther downstream), but it also requires that those with home insurance covered by flooding get paid, which in turn causes others' insurance rates to raise slightly. Then, we have issues with economics of people being unable to afford house insurance, and other governmental spending to fix issues that could have been prevented in the first place.
Furthermore, we go on pretending that what is currently occuring is good, and that we also can play God Almighty and control nature's forces (which are unpredictable) by building more levee and flood containment systems. Even more, we have to deal with degradation of streams, which results in decrease aquatic species (yes, that means less fish for us to eat), and thus greater food prices.
This is not a worst case scenario. It happens every year, across the country, with seasonal rains and flooding. It is occuring more frequently in recent years due to the greater severity and intensity of storms. So, this is not an issue to be taken lightly. This affects all Americans at their pocket books. Unfortunately, leadership in many locations continues to evade these issues, rather than confront them head-on, and educate the American public about the problems. Then, the American public, which is wholely good at heart and in intent, could begin to demand better development methods. Grassroots. Democracy. We need government for regulations, but we need the bottom-up to actually understand and retain the issues that are presenting themselves to us.
