A long 3-wide water canal, with some rabbits flowing down it. The entire canal has only one source block, on the far left.
Lava flowing in a 3-wide lava canal. There are only 3 source blocks in this picture.
Canals filled with chocolate and honey from Create
On the left, the junction space is not "in a canal", so the water level falls further
My other mod "Give Me Water Or Give Me Death" can change the max distance between farmland and water, allowing for wider spacing between the canals.
You can see the fluid drops much more at the planks, because planks are not a valid base or wall block for a canal.