"The roots need a lot of water."

Translation: Rødderne behøver meget vand.

[RowanM.1]

There was another question where "a lot of" had to be translated with "meget af". Not sure why that isn't used here.

[Meredydd]

Mange was not accepted. What is the difference from the grammatic point of view?

[Xneb]

"Mange" is used for countable or plural collective nouns:
"Hvor mange penge?" = How much money (lit. How many monies?)
"Der er mange køer" = There are many cows

"Meget" is for uncountable nouns and to describe the degree of an adjective
"Meget vand" = A lot of water
"Hun er meget smuk" = She is very beautiful

Here, "vand" is an uncountable noun, and so takes "meget"

[JamesTWils]

So, similar to the distinction between much and many in English, then.

[yosjp]

Rødderne trænger til meget vand. I do not understand, why this is wrong.

[shanne11]

why not masser af vand?