It now seems that they’re past the ‘indiscriminate bombing’ stage and into the ‘indiscriminate flooding’ stage, to be followed by the ‘indiscriminate victory’ stage.
Flooding the tunnels would not be indiscriminate, it would be directly against Hamas and something they should have done in the beginning assuming this would work. There was some question though as to how effective it would be because they weren’t certain whether the water would drain away quicker than they could flood it. Apparently the rock there is somewhat porous.