Translation:He wants to drink a little bit of water.
"He would like to drink a little water" is also a correct answer. "想" can also mean "would like to"
"A little bit of water" is not good English. "A little water" or "a (little) drop of water" would be better.
This is a long way of saying it, but the exercise doesn't accept just "a bit of water", which is more common
Nothing wrong - just suggest it, and in due course they will add it to the list of acceptable answers.
He wants a little bit of water to drink. Shouldn't that be allowed too?
That would differ in the meaning. "Drink a bit of water" -> He wants to drink it right now "Bit of water to drink" -> He wants some water, and could drink it later
Also "some" water. Ive never asked for a "little bit of water" in my life
We should be able to drop the "drink" as its not a natural English sentence with it
他想喝一點兒水。 In Taiwan we seldom use "兒" here, and sometimes even "一" can be omitted: 他想喝點水。
More like 'sip of water'.