Following up on Water and Bugs

Question

I appreciate your answer on water and bugs, but do not fully understand it. As far as I understand, bugs have only been seen under very special circumstances - drying out water under a slide, and then only trained eyes can distinguish a speck from a bug. In your opinion, what does the fact that a scientist can find it mean to me? If I look at my water and don't see anything, isn't that enough? Or do I need a filter becuase someone reports being able to see it?