My six-year-old has never had much interest in drinking fluids, and has recently had problems with passing faeces (i.e. constipation), which will not have been helped by this inattention to drinking.
We provide water with every meal (as a family we generally have just water, but squash or ribena occasionally - I don't know if she drinks more when we have those sweet drinks) although she is at school from 9am-3pm. Chiding her to drink more has little effect as she is strong-willed and independent. How can we encourage her to habitually drink more fluids? She generally takes about a third to half of a cup/beaker at a mealtimes, and will sometimes ask for a drink after school, which again will be less than half drunk.