Kylake,
Of course it happens in every single place where water runs into the river and then the river runs into the sea. It is how nature works. And your California comparison is insulting to Jamaica. "The difference is"? What difference?
As for the testing, yes you do stand corrected. As has been stated multiple times now in this thread, testing is being done by multiple agencies including the local NEPT organization. In your post you stated that testing is being done as rjonsun has stated.
And when there is a problem, public notices are made - so you stand corrected there as well. Actually living here lets us be aware of these warnings, but they occur very rarely and only after such events as major tropical storms and hurricanes. The water plant was designed to even handle events such as tropical storms and hurricanes. It was designed with help and support from USAID and the European Union.
A little more than average rainfall is nothing. All that does is help to keep the water treatment plant from facing drought conditions.
If you are truly interested, I posted those links so you can contact the professionals directly to end your worry and speculation about nothing.