I'd definitely take data on water UE with a grain of salt. Keep in mind that for an average player, it can be quite difficult to get a decent thunder team together, so unless they have a strong incentive to do so (Kirin or multiple SSRs), most just avoid it entirely. This can have a negative effect on water UE points for mid to average players. Conversely, note how insanely high the strong players score are in the rankings compared to the last few UEs. It's just an effect of the Thunder team meta, imo.