I used the bottled "Spring Water" not Distilled or Drinking Water for a while because I had a Very High Nitrate Level but only to mix about 50% into tap water, but I found out this is not a good idea as it does not appear to be a good thing for the fish in the long run. It is too hard to get a constant mix and the use of Amquel+ in the water to remove the Nitrates was just as effective. There should be no way you would consider the use of all of your water as the fish and plants do benefit from some of the properties found in water that is not processed in this manner, and processed it is. Plus if you have shellfish like shrimp or snails they will appreciate the calcium levels that tap water can have that the bottled water will not contain.
It is just not a good idea unless there is a definite reason why the city water cannot or should not be used for human consumption, in which case, you have a much larger problem than what to fill the tank with, me thinks.
Welcome to Fishlore.com. It is a great site where we do try to answer the questions of those of us who keep fish and care for our little friends. There are some great people here and I hope your experience here is as pleasant as mine has been. Again, welcome.
Most folks don't use bottled water because it would be expensive, and it's not necessary. The ph of bottled water might be very different depending on the water you use, and could cause ph swings which would not be good for the fish. Also, depending on what type of water you use, some of it has been stripped of all the trace elements which is benefical to your fish. Some folks mix R/O (reverse osmosis) water with tap water because of nitrates, or they have a ph in their tap water which is too high or too low. Most tap water is fine for your fish. The ph issue is not usually a problem for your fish either if they are slowly acclimated to a different ph. The problem you have with ph is when it fluctuates more than .2 in a short period of time such as when making a water change. This sudden ph fluctuation can sicken and/or kill your fish very quickly.
I hav 6 2litre bottles that I fill up with tap water and use at each water change, the water sits 4 a period of about 6-7days with the caps off and this allows the chlorine in the water 2 evaporate out of the tap water my fish seem 2 love this water lol and it also avoids havin 2 use any chemicals 2 get rid of cholrine