It is a bad Idea to use Water as Enderman killer anyways, since as soon as someone builds close to it the Endermen will teleport out en mass. Fall Damage is much better since you can switch that to 1 hit kill for an EXP Farm.
You describe a different type of farm, i am not interested in exp, i am just interested in enderpearls and for that killing quickly spawning enderman with water works just fine. In addition the rules say to not build near existing builds, so if someone actually builds that close that enderman teleport out, he/she did that with intention.
Independent from that is it pretty bad experience for players, when they start building a farm and then a mod is added, which has hugh potential to create issues or destroy things (e.g. water source blocks removal from mob farm -> farm broken or water source block moves down into your base with complex redstone and destroys it, fun?) and there is not even a hint for that during the addition.
So please disable those liquid physics now.