Stains are much more difficult to get out once they have set, so if you spill water, get to work immediately. Saving the chore for later makes getting rid of the stain much more difficult, if not impossible.
It may be tempting to use more water to spread and dilute the stain or to soak the cushions in a cleaner, but doing this makes the stain worse. Targeted cleaning with a damp cloth is more effective.
If you have a microfiber couch, use a baby wipe. For leather and suede, you may need to purchase a specialty cleaner. For other types of couches, try a 3:1 ratio of baking powder to club soda or denatured alcohol; just make sure to test it on a small patch first.
Dry the couch quickly after cleaning it. Turn on a fan if you have one, or you can even use a hair dryer on certain spots that are wetter than others.