I love Vivian & Cora, and I like Thetis (or I like the look of it, at least)
I think Lorraine, Lynn, Morgana, Marina and Brooke are all solid, and Morgana is an especially unexpected pick
I can't take Aqua, Aquarius, Misty, Rainie or Nixie very seriously, sorry.
Delta is… interesting. I'm not sure if people think for of the airline, though. Raine is fine… totally acceptable, just nms.
I am torn about Una. On one hand, I appreciate its background, and I do like the sound of it. On the other hand, as a Spanish speaker, I can't really get past the "one/ a" translation.
For boys, I love Morgan and Adrian! River is nmsaa, but I like it more than Ocean.
My favourite water-related names are Mar and Itsaso, both for girls, and they both mean 'sea'.