I've just had a quick look in "Baby Love" by midwife, Robin Barker. She says a 6-9 mo should have 120-180ml; 2-4 bottles a day or drinks from a cup as well as 3 meals a day. For 9-12 mo it says 120-180ml; 2-3 bottles a day or drinks from a cup and 3 meals.
edited to say this is on page 123 of the '07 ed.
I've never used this info before, but know that my midwife has told me 6-8 wet nappies a day is what to look out for - but when that changes to fewer I'm not sure???
Anyway, it sounds like Alex should be drinking between 240ml (2 x 120) and 720ml (4 x 180) a day - a huge range. I wouldn't worry unless there are other signs of him being unwell. I am pretty sure it's normal for a bub to learn to last a full night with out a feed.

j/k My daughter was 11 weeks sleeping through the night; my son at 5 mos is still waking at least once, mostly twice.
HTH