How would Water Whip interact with Wall of Water?

Question

Let’s say a Way of the Four Elements monk wants to use his Water Whip elemental discipline spell to grab an horrible sorcerer standing behind a Wall of Water (from the spell found in the Elemental Evil Player’s companion).

Water whip:

You can spend 2 ki points as an action (as per the errata) to create a whip of water that shoves and pulls a creature to unbalance it. […] On a failed save, the creature takes 3d10 bludgeoning damage, plus an extra 1d10 bludgeoning damage for each additional ki point you spend, and you can either knock it prone or pull it up to 25 feet closer to you. (PHB, p. 81, emphasis mine)

Wall of water:

You conjure up a wall of water on the ground at a point you can see within range. You can make the wall up to 30 feet long, 10 feet high, and 1 foot thick, or you can make a ringed wall up to 20 feet in diameter, 20 feet high, and 1 foot thick. The wall vanishes when the spell ends. The wall’s space is difficult terrain. Any ranged weapon attack that enters the wall’s space has disadvantage on the attack roll, and fire damage is halved if the fire effect passes through the wall to reach its target. (EEPC, p. 23, emphasis mine)

How would this work? Would the wall deflect the spell, or cause both sources of water to merge in any way? Would the whip pass through it freely? If so, how would the “difficult terrain” affect the distance over which the target is pulled, if at all?

Answer 1

As far as the rules are concerned, wall of water won't affect water whip in any way.

Water whip isn't a ranged weapon attack, and it doesn't deal fire damage, so the only part of wall of water that might make a difference here is that it is "difficult terrain". So what's difficult terrain? It's this:

Every foot of movement in difficult terrain costs 1 extra foot.

However, this is taken from the section about the movement of a creature using its speed on its turn, so it doesn't apply to any and all movement.

So as far as the rules are concerned, water whip will be completely unaffected by wall of water. It's up to you if you want to change this; as always, you can make whatever houserules you deem appropriate.