Any update on this? I noticed you posted it about a month ago.
My first thought is to check the jar/container and see if there is any warning for the cat getting too much powder. However, I’m not sure how much of a difference 1/2 a tablespoon of water would make. I think there would be more of a concern if you were actually giving the kitten too much or too little powder, because the powder has the nutritional value/level the kitten needs for the time being. I’ve never had a super young kitten, so I’m not sure if you are allowed to give them plain water. I would just try to find a way to keep him better hydrated if he is constipated.
My second thought is I’ve heard that really young kittens need stimulated to help go to the bathroom.
There is a great YouTube channel with tons of information on kittens. The channel is Kitten Lady. She tells all about kitten development, growth, how-tos, etc. I would recommend seeing if her video on bottle feeding would help.
Hopefully your kitty is doing better now!