This is one of the few requirements that got less strict since the previous incarnation of Weight Watchers. We used to be told that only plain water counted toward our quota, and one leader even told me that for every cup of coffee I drank, I should have an extra glass of water, above and beyond the regular requirements. Now most drinks, including coffee, can count toward our liquids. This may be because there was never much evidence that all that water was necessary. Alcohol still does not count.
Even with the stricter requirements, this has always been an easy one for me. Even though my family was a heavy Pepsi-drinking crowd, I usually preferred drinking water, especially with ice, so as long as I drink when I'm thirsty, it has been easy to get my water in. Now that I'm on Weight Watchers, I hate to waste points on beverages, so most of the things I drink are calorie-free: Water, plain seltzer, iced tea and coffee (though I always put a splash of half and half or soy creamer in that last one). I think this requirement used to be harder for the Diet Coke fanatics, but now they are home free. It may be better to get in the habit of drinking more water and less other stuff to avoid getting too much sugar, caffeine, artificial sweeteners, artificial colors, and all that other junk. I have a filter on my refrigerator and one of those stainless steel water bottles in an effort to stop cluttering up the planet with so many plastic bottles, but I still buy bottled now and then for convenience.
I just got out of the pool about two hours ago, so I swam in water (highly chlorinated, so I tried not to drink any of it), showered in hot water, and am now drinking a tall glass of water. It's pretty amazing stuff.