Here's the latest thing the new formats let us do.
The key thing to note here: The two water pieces are the
same (meta)object - set "default", piece "water". This piece allows for variable sizing. In general, water, one-way walls and updrafts allow for this, as do some (but not all) one-way fields.
Specifically, here's the relevant part of the level file:
# Interactive objects
OBJECT
SET default
PIECE water
X 504
Y 52
WIDTH 32
NO_OVERWRITE
OBJECT
SET default
PIECE water
X 488
Y 32
WIDTH 64
NO_OVERWRITE