a normal sized coke can is 250ml so a inch and half from the top of a can of coke filled with water would be about 200mls.
coca can is not 250ml but
330ml if you not happen to be on a plain and get a "single serving sized" one
cut that crap with how much per 48h or what ever.
stick to this rather: water as soon the soil surrounding dries up and stop as soon the soil starts to get lightly soaked. don't water till the soil is flooded away
if you want to go kinda high-tech try this:
-get a bucket, 5-8 gal size or bit bigger if you like
-see that you get a lid for it
-drill a hole into the bottom rim of the bucket and attach a piece of garden tub to it
-plug this tub on the far end and pinch a tinny hole in it and place it close to the plants stem
-if more water is needed pinch a further on in
-you get the best results if you cover up the top soil with foil to keep the moister from evaporating