At this point, I don't think manufacturers have a clue. The toxin is part of the algae, not a contaminant. The algae makes it.

One site I looked at had this comment:
Animals do not eat the algae as a food source, and that is why it builds up in some water sources. THEY know, it is not to be consumed, and it is only humans who have attributed food or other value to it. Even fish, only certain tropical fish eat algae...not all of them. I think the algae eaters have the ability to handle the metabolism better, etc. So the hints are there in nature already IMO.

We double filter our water, up there which removes the algae for drinking.

This toxin discovered is cummulative... so time is also a factor in dilute situations.