Using your smartphone and a variety of items you can buy for cheap or find around the house, you can see all the little microbes that might be floating around in a body of water, be it your sink water, pond water, or puddle water.
You'll need a bright flashlight, some white paper, a piece of clear plastic, some scissors, a laser pointer, a smartphone, some poster tack, a small lens, and a water sample.
You'll place the paper over the flashlight, which should be standing up, and then you'll cut the plastic into strips to create microscope slides. Afterwards, put some of the water sample on the plastic slide, then add another strip of plastic over the top of that.
Now, you'll be able to place your lens on the back of your smartphone's camera with the poster tack and use your smartphone to look at all the little microbes in the water sample with the flashlight turned on.
Pretty cool, eh?