||Without getting involved in the halachic question of water filters, I would like to relate my personal experience when I tested my own water in Flatbush.
First, I cleaned out a glass and filled it with water. Then I took a piece of t-shirt and wrapped it around the water faucett. I let the water run for about 5 minutes through the t-shirt. (Believe it or not, the t-shirt turned a filthy yellow in just a few minutes. I pretty much resolved right then that even if I don't see any bugs I should get a filter).
Then I carefully removed the t-shirt off the faucett and placed it in the glass of water. You could not imagine the kind of garbage that floated off the t-shirt and into the water. and yes! I did see at least a few of the bugs as they were described.
PS. We now drink bottled water.