I'd love to know where this rumour has been started. The ship does not take ANY water onboard from land, except bottled to sell you later. All the ship's water is produced thru a reverse osmosis process directly from seawater. That is something I have not read on the boards, but found out in person, right from the ship's engineer. I have no objections to drinking the ship's water. If you're particular, the water at the deck 9 stations is double filtered.
As for soda, it is also free at the end of the buffet lines and at the deck 9 station right next to the Mickey Pool. You're welcome to bring either onboard, but I see no need to do so anymore, short of you wanting a particular soda product other than Coke products. There are plenty of cups with lids available at the deck 9 station so you can fill them and take them elsewhere. The only place you pay for soda now is at the bars.
As my wife, wdwlvr, said above, for our most recent of 6 cruises, the 10 day, we brought sport bottles, packed them full with ice, topped with water and had drinking water for our excursions every day that stayed cold for the duration of the day's travel. Just make sure they are wide mouth ones so you can get the ice in.