The coach didn't need to be rude, especially if you didn't know and she couldn't explain why.
Here might be why...
IP Phase 1 as written is trying to help us achieve a healthy Acid/Alkaline (ph) balance. Typical tap water ("still" water) has a pH of 7, which is neutral. Typical carbonated water has a pH of 3 or 4, more acidic. Even though your soda stream probably just adds carbon dioxide (and not any salt as found in store-bought soda water), even just the carbon dioxide puts an added stress on the kidneys, as the body tries to rid itself of the gas. This is a link to a short article on this:
http://www.livestrong.com/article/11...s.-flat-water/
I also tried to attach a file that I found at a site called ihpweightloss.com, which has the official IP logo on it. It shows still water as alkaline and then has soda on the high acid end.
Before IP I drank Perrier (carbonated water) to replace a desire for soda. I stopped it altogether when I started IP; it wasn't as bad as I feared, and I can usually get in 3 liters/(100 oz) of still water each day. Sometimes I warm it a little in the microwave or make sure it is not real cold which makes it easier to drink and "enjoy".
You've made lots of other changes during your first 4 weeks on IP. Hopefully those have become a routine by now. Stick with the rest of the plan as you have been. Then decide if carbonated water is what is going to keep you on or if you are able to give that up until Phase 4. You could try weaning yourself off the carbonated water by getting in 32 oz of still water then having 8 oz carbonated as a treat (wow, carbonated water as a treat sounds kind of crazy
).
You could also consider changing clinics, if that is an option, and asking any new clinics the carbonated water question, using their ability to explain it as the criteria for which clinic to pick.