Once you get your Water team to a decent state, I highly recommend working on the flipside of your Water team - Wind. It's a team you'll literally only be using against Thunder content. Even a just Wind Grid will get you easily through everything except Thunder GO, and even that will be mostly doable as long as you have the Grid to support it.

Light/Dark/Fire are fine too as a secondary team, if you have any great SSRs for one of those.