Am I missing something with the available stock assets, I just tried to add some water or a sea to my test level and cannot see anything I can use quickly?
There is a water shader in Starter Content.
There are water materials and glass material in the Starter Content. However, water materials are solid (no transparent) while the glass material is static. A quick solution is copy-paste the Base color part from water material into glass material and you have a moving water surface material. Then tweak values if you want.