Anywho, whether you are as enthusiastic about gardening as I am or not, rain gardens don't have to be difficult at all.
There are a couple things that need to be explained first. There are two types of basic surface, pervious, and impervious. As you may or may not already know, pervious means that things, mostly water, can pass through it (permeable is another word, just not used in this case). Impervious means that water cannot pass through it. Much of our "civilized" world today is covered in impervious surface. For instance, where I live, Hampton Roads, it is said to be on average, 60% impervious surface. That means, of all the land in this area, well over half is paved or somehow covered with surface (buildings) that will not absorb water, and instead contribute to runoff, often directly into stormwater systems and into the Chesapeake Bay. When you add pervious surface into the equation, rather than immediately stream from building to parking lot to stormwater drains to the Bay, some of this water will instead be absorbed into the ground, where it can be filtered prior to entering the Bay (or whatever your watershed is). Add plants to the equation and BAM! Now, not only is the water absorbing, but you have increased its porosity, with root systems, and the ability of the soil to absorb goes up, as the plants suck up the water. Now, this cleaner water can also be transpired by the plants, back into the atmosphere.
Essentially, all you need to do in order to establish a functional rain garden is to watch and see where rainwater runs off from your home (or workplace!). At our house, most is from the gutters, and because our house is on an incline from the road, it runs from the gutters, down to the road. Ideally, we would take the driveway and make it a less pervious surface. However, this can be a bit more expensive. I have seen lovely things done though, were you can mix in pavers with bits of grass-like plants (anything sturdy and short, ideally something that doesn't need to be cut), or concrete with spaces.
There are also several pervious asphalt options, some of which can get pricey. There are few options listed here.
Back to gardens though. It is always best to use native plants, in any gardening. If you are unsure what is native, do a google search for your area, or talk to local garden clubs. They may have a list available. These plants are best, because they will likely require the least amount of care, once they are established. Because they are used to the local conditions (rain, heat, cold, etc), they should require minimal watering from you and still look good (or at least stay alive). These are my kind of plants :)
Gutter downspouts are a great place for this, if there is somewhere to put in a little garden. Often times, you may see them in drainage ditches. Our city has recently started planting them, on a slope, in the middle of the road. Here are some lovely examples of raingardens:
