Both DD1 and DD2 wouldn’t drink left to their own devices. With DD1, we give her milk and biscuits with her meds in bed, to stop that first hunger drop attack. Then we give her a drink at every meal, and half way between meals. She has another drink with her evening meds. We have to prompt her to drink between meals. She and DH run much hotter than me, so they are always complaining it’s too hot, and sweating far more than me. Both of them need to drink more than me, although I have to keep well hydrated for a health problem.
DD2, even when she’s breastfeeding, might not have had a drink all day by 4 pm. She would never use school toilets, so she didn’t drink at school - I guess she got used to it. Also, her sensory processing is a bit strange - so, it could be something to do with that? For instance, she can’t stand her nails being level with the top of her fingers? She has to have long nails? Likewise, she can’t cope with gloopy liquid medicines, whereas food textures don’t bother her.
DD1 is diagnosed with sensory processing disorder, but she has the common problems like loud noise, hand driers, clothes labels (as a child), hot baths, etc.
The trouble is while DD1 has obvious learning disability and challenging behaviour, it’s easier to tell her to do something and she’ll do it, most of the time; whereas DD2 is obviously mentally ill, but much more articulate and able to argue back, deflect, and lie.