Amazon offers the Glaceau Smartwater 1-Liter Bottle 6-Pack
for $5.99. Order via Subscribe & Save to drop it to $5.69
and bag free shipping
. That's about a buck less than you could expect to pay in local stores, although we saw it for slightly less last month.
Note: Be sure to cancel Subscribe & Save once your order ships or you'll be billed for subsequent shipments.