When looking at flowing water with the F3 debug display information turned on, the water is supposedly minecraft:flowing_water. However, it is impossible to use /setblock to place a minecraft:flowing_water block, and /execute cannot be used to find such a block. Instead, the water is found with this command:

/execute if block [X] [Y] [Z] minecraft:water

Also, #minecraft:water is said to not be a block.

The following commands (which don't currently work) need to work to match up with what F3 says about water blocks:

/setblock [X] [Y] [Z] minecraft:flowing_water

/execute if block [X] [Y] [Z] #minecraft:water

/execute if block [X] [Y] [Z] minecraft:flowing_water[level = 5]