I use filtered tap water. Tastes great, and is much less expensive and better for the environment than buying trucked-in bottled water, which is often just filtered tap water anyway. Try one of these:
http://www.amazon.com/Pur-Stage-Pitcher ... 000QR95CQ/
http://www.amazon.com/Pur-Vertical-Fauc ... 0009CEKY6/
Key is change the filters when it says. The faucet mounted ones are nice because you can use a 3-stage filter that adds trace minerals for taste, which is actually excellent.
I use the faucet-mounted model to fill an airt-tight glass pitcher which I keep in the fridge. Thus, the water has less contact with plastic. Also, the faucet-mounted version lasts 100 gallons, so you shouldn't have to replace it very often.
Hope this helps, and happy tea-drinking!