The most common and most likely answer to this crossword clue is the 11 letter word DESALINATED
I've seen this crossword clue in The Guardian
D
E
S
A
L
I
N
A
T
E
D
More clues leading to the result DESALINATED
Buddy explains!
The straight part
We know that "harder to float in it" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case harder to float in it = desalinated.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does DESALINATED mean?
DESALINATED verb- To remove the salt from something, especially from seawater for use in a domestic water supply