I've been using Brita-filtered water in my small aquariums (6G and 10G) since August 2006 (I change out several gallons a week from each tank, and have used gallon water jugs put aside with water ready for each change). If i can drink Brita water, they can surely swim in it (and I use Prime to condition their water). Using a filter like a Brita will be cheaper than buying spring water. Our tap water is okay (at least to bathe in), but it is hard and has plenty of minerals which would be leaving white deposits in the aquarium if I didn't run it through a Brita filter first.
If you can't find the pure amonia (no soaps or scents), but you have a friend with an established, healthy aquarium(s), you could run the filter on that for a few days to help the filter gather good bacteria. Also, your friend might give (or loan) you gravel or rocks from their aquarium that also have good bacteria established on them. Just some alternatives to speed up a cycle.
If you can't find the pure amonia (no soaps or scents), but you have a friend with an established, healthy aquarium(s), you could run the filter on that for a few days to help the filter gather good bacteria. Also, your friend might give (or loan) you gravel or rocks from their aquarium that also have good bacteria established on them. Just some alternatives to speed up a cycle.