Here's a short video I took to show what lives in a drop of water. Magnification is 100x. This is typical of most water you find in the wild. Its also available on You Tube and here's the link; http://www.youtube.com/watch?v=Pphn08NjTDE
Here are a few still photos of different water creatures. The first three show a species of Vorticella connected by fine threads to the root of a Lemna (duckweed). The first photo shows a few Lemna "infants" floating to the left and at the bottom. Vorticella feeds on tiny creatures such as Paramecium, Volvox, and others which you can see in the above video. These are 100x magnification.These creatures can all be removed with a good water filter. Moving water does not contain the same abundance of life forms as still water. If I were drinking water from this pond I would use a good pre filter to keep my filter elements clean.
This photo shows the larva stag of Cyclops or similar species, a tiny crustacean. Again its 100x magnification.
This photo shows a Diatom or Desmid. I'm not certain which or its species name. More Vorticella at the bottom left.