DD does not drink alot either, is a family trait, I don't and my dad is the same - I just offer whenever we have a drink (get DH to remind me to drink), and try to encourage 'tea parties' where we play picnics and drink during those - is good for me too. Apart from that don't see there is alot else can do, trying too forcefully will only put her off, I notice she does drink more when us hot so does feel the need to drink, so I don't worry too much figure guidelines are based on averages so some will need more and some will need less.