You’re dancing around the issue.
Unless you believe that the copepods were spotted immediately (i.e. they were not present prior to 2005), you are forced to choose from these conclusions:
1- Between the time copepods appeared in fresh water and 2005, all Jews ate shratzim
2- It is not assur to drink unfiltered fresh water, despite the copepods
3- B’derech nes no copepods ever made its way into the water consumed by a Jew