Rain. Think about what a great idea it is.
No engineer ever conceived of a system for the distribution of water anywhere near as elegant. No pipes to leak, no pumps to break, powered by the sun, available nearly everywhere. Just set up something to catch it and store it in.
Self-cleaning too, and what's more, it cleans all the stuff it falls on. Sort of a side benefit.
Oh, but it's so inefficient! Think of all that wasted rain that falls into the oceans! Of course, if you decide to put an island out there, bam- fresh water. No need to run a special trans-ocean pipeline.
In reality, of course, my conception of rain as being beneficial is mainly because it was there before we were here. Life on earth grew up around the fact of rain, just as it has sunlight, and an atmosphere. Sunlight wasn't always filtered of deadly radiation by ozone, however, and the atmosphere didn't always contain oxygen. These things change over time, and life manages to keep up with (or cause) these changes. We (living things) are nicely suited to earth because we grew up together.
I'm a believer in the anthro-centric theory of the universe. As I understand this, the explaination for our being here is because we are here. If self-conscious, thinking beings capable of posing the question "why" had not evolved, there would be no reason for us whatsoever. Wherever you go, there you are.
This can be deeply unsatisfying to those who think there must be reasons for things, but in all honesty, if you really believe that there are reasons for things, and don't fall back on some mystical, unknowable reasons for things, then I think you have to admit that our experience of the universe is all about us experiencing the universe. There's something out there, and we are somewhat uniquely (as far as we know) able to enjoy it.
By "something out there" I mean that I believe we aren't just living in a dream world. I do believe that that "something" that is outside our minds is only poorly described by our words for it, and only vaguely apprehended by our feelings toward it. In fact, the fact that our minds are part of the "something out there" (physical world) makes this even more interesting. We are, like rain, a natural phenomenon. Scary, innit?