Would it be at all possible for a creature to generate or store water and expel it with enough force to repel enemies or hunt? I know there are already fish that do it (archer-fish) but I'm looking for a possibility of a creature that lives on land and can shoot water that it stores/generates hard enough to repel a large creature such as a bear or lion or uses it accurately to hunt large prey like deer or similar.
The bombardier beetle may be a good place to start for concepts. Wikipedia article Here
The beetle generates two liquids that when combined reach a high temperature and is mainly used for defense. Scale it up, and it would be a formidable creature.
Injury (in combat, whether for defense or hunting) is a matter of delivering energy. A stream of water is not a particularly efficient mechanism for doing this. Air resistance to a stream of water is extreme (as the outer layers of the stream ablate off), and scales non-linearly with the velocity of the water.
Moreover, whatever tissue is used to focus the stream must be capable of withstanding the pressure and erosion involved with expelling the water. Generally, parts of animals used to expel water (mouths, urinary tracts) have mucous membranes to protect against damage, but the greater the force required, the greater the damage to the creature expelling it.
Water is also heavy. Carrying or propelling water uses an enormous amount of energy, and is generally only beneficial when the water is meant for the survival of the carrying creature, not if it is intended to be used. The archerfish's use of water as a weapon is simplified by the fact that it doesn't have to bring it along to wherever it intends to use it.
reality-check as a tag, I would say that it's hard to envision any scenario where such a defense/hunting mechanism would be an evolutionary advantage that outweighs its obvious and immediate drawbacks.
reality-check, hunting still seems wildly unlikely (you'd be expending a lot of a valuable resource without any assurance of gaining it back) but there are a number of creatures that use similar approaches as defense mechanisms:
- As mentioned above, the bombardier beetle uses a two-chemical exothermic defense
- The horned lizard shoots bad-tasting blood from its eyes into its predators' mouths (though specifically canids).
- Skunks, famously.
- Lots of creatures pee as a defense. This can startle a predator, and often smells bad, which can cause enough hesitation for the prey to escape.
This generally isn't pure water, and depends on chemicals added by the creature's biology to make it an effective defense, but the groundwork is there.