Water is the deadliest hazard in Worms. If a Worm walks, falls, or gets knocked into the water, they will instantly die from drowning. In the first generation Worms games, there are different water appearances. For example, the Hell Theme replaces water with fire/lava (the effects of drowning are always the same, different themes only change the appearance of the water). However, in Worms 2, there is only water, no theme-replacements such as hell-fire. The water comes in different colors, though. But for the rest of the second generation Worms, and for most other Worms games, there is only blue water, nothing else, no matter what theme it is. Also, the commentary panel shows up when a Worm drowns (in any Worms game). The water could be quite good for you (by using the water to kill an opponent, such as knocking an enemy into the water), but it could also be quite bad for you (your opponent can knock you into the water too, of course). And walking into the water is a terrible idea - Worms is not a fishing game, so don't even think about doing it!
Water has many uses. Mainly, you can knock an opponent into the water. But you can also use the water to get rid of hazards, such as Mines, by knocking it into the water with a Baseball Bat. And you can use a Nuclear Bomb or Indian Nuclear Test to raise the water and drown the enemy. That is the best use of water, when most (if not all) enemy Worms are near the water level. Water is more dangerous than any weapon, and this may be why the Nuke is one of the series' most powerful weapons. Water weapons (weapons which create dynamic water) were introduced in Worms: Revolution, and made a big change in the gameplay of Worms.