How do water-based defenses work in Die2nite?

Water turrets is the only defense that will consume water each night. It only does so if you have voted to upgrade it at least once, and if you don't have enough water in the well during the attack, you won't get the benefit of any of the upgrades (it still provides the base defense). The amount of water is equal to the amount it consumes, which goes 2-4-6-9-12 based on how many times you have upgraded the turrets. Towns may upgrade the water turrets but intentionally take all the water out of the well and store it in the bank unless they need the upgraded defense that day.

None of the other water defenses require water from the well, and they will all work regardless of the amount of water in the well.

Contrary to what the wiki implies, building Plumbing has no effect on the cost to build water-based defenses, nor on the nightly upkeep of water turrets.