I suspect I possibly worry a little too much about this as DD is in cracking health, never had anything like a urine infection. She just does not drink.
On a typical day she will have milk on cereal or porridge then after school will come home with drink untouched in packed lunch, perhaps have a sip of water or milk with dinner and refuse to drink any more. Has been known to drink milk at childminder's on day she goes there. She eats bucketloads of fruit and yoghurt though. Occasionally she gets thirsty and downs a few glasses of milk at once.
It seems she is getting enough liquid, but AIBU to gently nag at her daily to drink more? Bearing in mind gentle nagging has zero effect!