[cypher]

Hi & welcome to HC.
I don't think putting antibiotics in water is easy or accurate tbh, it's hard to know how much they will drink & if they will get the full dose.
Most people put it onto something like porridge or baby food or even a little scrambled egg, basically some kind of soft wet food they see as a treat & will happily eat. Just a tiny bit on a teaspoon so you can be sure they get all the meds.
If you use baby food you need to check all the ingredients are ham safe though.
They can feel a little unwell on antibiotics so that may put him off eating or drinking quite the same a normal, you can give probiotics which help them deal with the effects of the antibiotics too.