Product review (4 stars): Your fridge demands it!
My old filter was so old (how old was it?!) that when i depressed the lever in my fridge, human blood spewed forth. Could have been elephant blood  they taste the same. In comes Water Sentinel, and lo, the macabre rivers run clean and clear, providing nourishing hydration for all my sweat-depleted needs. This is the most cost concious option, and a two-pack will last you an earth year. Unless you're one of "those types" who drinks, like, a billion fluid ounces a day, in which case, size up.