Wow, OK, didn't mean to get into the politics of water or anything (it is my profession though, so I could probably go on and on!). I just wanted to demonstrate how important it is to us as human beings. Now, of course, if you know me at all you will quickly guess that my mind translates this to birds and other wildlife. They depend on water just as much as we do. They have to fight off dehydration, just like us. They use it to bathe, just like us. Cleaning is important to ward off disease and parasites. Certain species of birds seem to just plain like to splash around in the water more than others!
I would say the #1 question I get asked by people who know I like birds (well after the "what kind of bird is this?" type question) is this: "how do I attract them to my yard?" Or another variation, "you seem to get a lot of birds in your yard, is there a trick?" And then I share the biggest "trick" of them all: before you invest in a good feeder, invest in a good bird bath. They are easy to maintain, not to mention cheap! Even after your food runs out, keeping a bird bath clean and stocked will keep the birds coming in.
Now, you might ask, what makes a bird bath "good." Just about any style bird bath can be used, but some will have more success than others. Trust me, there are a TON of different styles. The key to any bird bath is to keep it clean and the water fresh. Now, before you install a refrigeration unit with Evian water (nice mental image there!), know that birds aren't too picky as long as the water is (a) clean and (b) accessible.
A note about accessibility: deep dish style bird bath isn't very accessible to birds, especially the steep-walled kind, which for some reason, seem to be popular in big box stores. Bird baths that have multiple levels on the bottom are much better for birds. The reason? Birds are all different sizes and they don't really like to just "dive" into a pool of water. They want to wade in, get their legs wet, and then squat the rest of the way in. Kind of like me trying to swim in Lake Superior a couple of summers ago. You put out a big dish style feeder, your bound to get mostly big birds, like Blue Jays or Crows.. which are great birds, don't get me wrong, but there are so many smaller birds to get to see up close bathing. I especially love watching bluebirds (in case you can't tell, almost all of these pictures have bluebirds bathing in them!).
But Lindsay, you cry, all I can find is a big dish feeder! Or maybe you like the design of a particular feeder, but it still has the big cup style bottom. Never fear, I have another trick for you! You can create different levels on the bottom very easily: with rocks. I guarantee you will get more birds if you try this easy trick. BTW I love my bird feeder.. and the birds seem to like it too!
There is more to "water" in habitat, such as winter water supply, ponds, etc., but I think this is good start. I will leave you with one last thought: birds can hear running water from near a mile away (supposedly, I never thought to ask them)... how much better would a water supply be if it had an element of motion (fountain, waterfall, dripper)?