I think we used those in the water quality lab I worked in in my first year in college. It was for one of the two bacterial count tests we did, plus we also did Nitrate, Nitrite and potassium level tests. I liked the agar plate thing better than the other, old-fashioned e-coli tests, mostly because we had to make the sets to test for e-coli and it involved filling a small test tube with medium and trying to get into a bigger tube filled with medium in a fashion not to make a bubble. Bitch.
This was so long ago we were doing oral pipetting, no filter, etc. Because of our lab cat I got a hepatitis gamma globulin booster plus a typhoid booster (would have gotten the series if I hadn't already done that for overseas trips...).
The most interesting part of the project was that we also went out on a weekly basis and collected our samples from various points along the Miami river and Coral Gables canal system. We were always finding headless white chickens stranded at various points. At the time we called them "Voodoo chjckens," I didn't know about Santaria at the time. And we were disturbed to find cichlid fish in the waterways. Apparently about five years later they started finding piranha.