You need a Master Test Kit (like the one from Aquarium Pharmaceuticals, Inc.) and you also need to take some tap water direct from the tap and test it before you add anything to it (no dechlorinating agents ... nothing) for ammonia, nitrites, and nitrates.
If the readings are less than:
Ammonia 0
Nitrites 0
Nitrates 20
then you do not need any kind of bottled water. If the first two are at 0 and you have a Nitrate reading of over 20 but not over 40 you can lower it with the use of the right water conditioner, Amquel+ (it neutralizes ammonia, nitrite, and nitrates) but it should not be started until your tank is cycled as the hampering action toward ammonia will cause a stall in the cycle. (according to the fine folks at Marineland in re: Bio-spira)(but you won't have fish in the tank during the cycle anyway, right?)
If you have Nitrates of over 40 then you will probably need a partial fill of SPRING water, but I agree with Gunnie, not unless it is really needed as you are right there are minerals that are present in tap water that are appropriate for the fish to be getting and it is expensive with any size tank at all.
I used Spring Water in my tanks in the summer when the Nitrate levels around here got above 80 but now I am back to tap water and with real plants (the very best solution for Nitrates) have it down below 20 but in the summer months, I will probably have to go back to Spring Water.
Rose