Has anyone heard of the illness I am going to describe?

[Saltire]

and if so what is it called.
3 year old child, he does like to drink, and ,IMO , uses the cup as a comforter (he's 3) as he can go ages and not ask for a drink. Because of this, I don't feel he has diabetes (plus he has no other symptoms of diabetes)
His parents have had him at doc (who also doesn't think it's diabetes) and he's going to hopsital in a few weeks. the doc said that it's an illness whereby the kidneys need to take in far far more fluid than they put out (although his urine is almost as clear as water, so obviously working ok) and that therefore they have to let him drink constantly.

Any suggestion as to what it's called?

Diabetes insipidus. Not diabetes as such as no sugar/insulin etc involved. More of a malfunction of different hormones (i think) which causes the body to excrete excessive amounts of dilute urine.

Really, thank you. Does it also cause them to drink excessive amounts,

Also cna if affect development and behaviour?

I've only ever seen it in an adult, I wouldnt see any reason for developmental concern though. They drink gallons.
there is loads of into here

Dont know much about it but am just a nurse that loves to find obscure illnesses!

Dont ask me about phaeochromacytosis!!!!