Thought I'd put a quick update out. Thanks to KevinM and others for the responses. I put a keg into service for carbonated water with a dedicated tap and my wife and I love it. I didn't go with a new keg, just used one of my nicer 5-gallon corneys. I cleaned, sanitized, and rinsed it well before the first fill. I haven't bothered to sanitize it since.
Here's my process for carbonating:
About a week before filling, I start making ice and transfer to gallon ziplock bags. My keg fridge has an icemaker with a dedicated carbon filter. I don't keep any open food in the fridge, so the ice stays pretty fresh. When its time to fill the keg, I add three or four bags of ice and fill using a carbon block filter
. Once the keg is full, I cap and force carbonate at 30 psi through the beverage out post. After 10-15 minutes of vigorous shaking, the water is pretty well carbonated -- the ice drops the water temp to near freezing, so the CO2 dissolves immediately. I keep the keg on 30 psi and serve through about 10 feet of line.