What a good question, you (and by you, I mean me) ask! Tardigrades live in both aquatic and terrestrial environments; in fact, chances are, if you went out and found a good chunk of moss in your own back yard, you could find tardigrades in it. Several other tardigrade websites outline the procedure in detail, but it's relatively simple, using a microscope:

 

1) Get a sizable sample of moss.

2) Soak this moss overnight in distilled water.

3) In the morning, squeeze the moss over a Petri dish.

4) Look at the Petri dish under the microscope, and behold! The tiny world of water bears has become visible to you.