I don't know all of the details behind how they treat the water or why, but my first and best guess is that this is related to the weather that we've had. This is the kind of thing that you'll often hear come up in the spring. Link below from April 2014 has a reference to the fact that the water becomes particularly difficult to treat (but still safe) with runoff followed by cold temps:
http://www.ebrandon.ca/messagethread.aspx?message_id=828416&cat_id=3<:/a>:
If anyone knows anything more concrete, please share
Edited by Adam, 2016-02-07 21:02:59