If all the water in the world is blessed by theophony blessings (I am thinking hear mostly of the outdoor blessings or rivers, lakes and the sea) the fact is in a year most if not all of it will have been used by humans or animals consuming it, or will have evaporated and precipitated out again, so lose the special caricter of blessed water. This is my personal understanding if it, but as I said in my last post the repetition is for us as we need to be reminded of things, in reality it only happened once at the time of Christ's baptism in the Jordan, we are participating in that. Just as there is only ever one eternal liturgy, in to which we step each time we go to liturgy as we step outside of time, or through our baptism we participate in the death and resection of Christ.
As for the last question you asked about the difference between water blessed in church and other water the best answer I can give is to retell a story my Priest told us, which came form his grandfather (also a Priest). My Priest's grandfather had a disagreement with a pharmacist (I think I remember that correctly) over holy water staying fresh permanently. So they did a test, they sealed some holy water in a bottle and some normal water in another and left them for two years, after this time both were tested and the holy water was still as it had been when put in the bottle, the other water was not.
I do not know if there are cannons related to this, the services are not the clearest on the matter ether, however the Prayers of the Priest make it clear that we are today participating in the events which happened in the Jordan, not by our imagination but that we are there. Just as at each of the fests we are there in the happening, hence 'today' is a prevalent word in this Feast as in all of them, reminding us that we step out into the eternal now of God.