The women have finally agreed on their pact to withold sexual pleasures from the men in order to encourage them to stop their long war. The men have decided to attack the Acropolis in order to take back the treasury which the women had seized in order to act as another barrier to the men continuing the war.
The men have set fire to the timbers the women used to block the door and the women use the water, obtained at great effort, to both stop the fire and the men a good soaking which slows them down as well.
I think that the answer you are looking for is water. There is certainly a part in the play where the women are throwing water on the men, and it is at least partly to make the men less aggressive.
This happens when the old men are trying to set the Acropolis on fire so that the women (who have taken the area over) will have to leave. The women end up throwing water all over the men to get them to stop what they are doing. The women are successful and the men leave.