This is the icon on the left lower toolbar to create  volumes. Use it with the BSP to make the water volume. You will most likely need to make a subtracted space for the water to reside in first.

You can make the subtracted space, then leave the BSP in position and make the water volume if you want, then, lower the water volume a little.

For now, use the default settings for water volume.

 

This will get you to the place where you can have someone make a splash, fill in and drown or swim, etc. But the surface needs ripples and this is where a special actor comes into play. Select near the water volume and place a FluidSurfaceInfo.

FluidSurfaceInfo is a plane that will be the surface of your water. So set the location and size appropriately.

Here is where you make the size:

Real-time preview and it should ripple ...

Here is a very good water surface shader you can use – this shader in package CPEffects1:

 

Set the timing of the ripples here [I want mine quite slow] ... 60 is the default setting

Test ... one of the neat things is, the water will increase the ripples when a player falls in.