Serviced my 335i SE last year June ish around 19k then just recently around 25k it kept on saying it needed +1 litre and then like full again on and off on and off. So I decided to put 500ml in to shut it up. Said full for awhile, but then it showed 3/4 full like couple of weeks later, so I put 250ml in. Now it hasn't bothered me since.
Does seem to drink a lot.