Add the DEEP_WATER flag.
Use DEEP_WATER flag for blocking vehicle water spawns.
Don't let marloss wipe out deep water.
Handle water properly when knocking creatures back.
Use DEEP_WATER flag for vehicle sinking.
Remove now-superfluous has_flag("LIQUID") checks,
Remove now-unnecessary SWIMMABLE flag check from quantum tunneling.
Use DEEP_WATER flag for diving into water.
Remove another now-unneeded SWIMMABLE flag check.
Use the DEEP_WATER flag when using > and < to dive/surface.
After handling water, don't then treat it like ground.
Use DEEP_WATER flag when displacing water.
Pruning more now-unneeded flags.
Use DEEP_WATER flag for is_divable.
Use DEEP_WATER flag when checking for underwater items.

Also, braces.
DEEP_WATER flag in can_move_to.
This isn't needed any more, thankfully.
Use DEEP_WATER flag for player knockback into water.
Another now-unneeded check gone!
No more unnecessary SWIMMABLE check here.