If you've picked up free samples at the bar or a Pride event, it's often water-based. Swing into your local pharmacy, and you'll probably find a wide array of water-based lubes.
Water-based lubes can be sticky, and may feel thicker than other varieties; that's usually a good way to identify them, other than the label. The biggest benefit of water-based lubes is that they wash off easily, both from your skin and your sheets.
However, water-based lubes typically dry out more quickly. You can add water or spit to re-hydrate them. You're probably best off adding a little more lube to the mix at that time too.
Water-based lubes can also cause cells to over-absorb water, which damages them, so receptive-anal partners are going to want to take good care of their backside after using water-based lubes.
One other thing to know about water-based lubes - because they are water soluble and wash out of sheets so well, they also wash off in places like the shower. If your favorite place to play is the shower, you'll want to look into silicone or oil based lubes.