How long does it take to drink a water bottle in Minecraft?

What better way than to measure from inside the game itself ? None, sir.

(Click to enlarge)

From right to left :

• A simple fill clock, running at 20Hz
  setblock ~ ~1 ~ air / setblock ~ ~-1 ~ redstone_block

• A command block incrementing my timer score if I'm in possession of a water bottle
  /scoreboard players add @p timer 1 {Inventory:[{id:"minecraft:potion"}]}

• A command block resetting my timer
  scoreboard players set @p timer 0

• A command block giving me a water bottle
  give @p potion

For the experiment I switch to gamemode 0. When I press the button and "drag" away from it, it sets the timer to zero, then gives me a water bottle. The bottle lands in my first free hotbar slot, which I have selected beforehand. This way I start drinking it right away, while the clock counts up. Once I drank it all, the water bottle is replaced by an empty bottle, and no longer triggers the counter. Thus, the timer indicates how long it has taken me to drink the water.

The results over 20 samples were :

Clk   N°
36    1
35    15
34    3
32    1

Barring a slight variation whose cause is unknown, the time to drink a water bottle is 35 * 1/20 = 1.75 seconds.

Edit: the same protocol applied to a standard cooked porkchop has shown similar results.