It can be literal if you are a diver, of course, but figuratively, it may mean that you are in a situation you don't control for lack of visibility, and the form would rather be in plural : en eaux profondes. Yet, as Aurélien says, it is not very common.
Other close expressions like "entre deux eaux" are much more usual (= managing to not chose between two opposite parties/opinions).
The words I am given to choose from (translating French to English) force me to use the English translation, "I am into deep water." I'm not aware of any English dialect in which this is correct. "I am in deep water" works, but "into" requires another verb: "I am getting into deep water." Furthermore, this is not how an American would typically express this apparently metaphorical statement. As someone else pointed out, "I'm in over my head" would be far more common.
The English phrase "in hot water" usually refers to the specific category of difficult situation wherein one has run into trouble with some sort of authority (one's boss, the police, a parent or teacher, a regulatory agency, etc.).
Not wholly dissimilar, perhaps, but not quite the same either.
That doesn't sound very natural to me (British). It sounds like a combination of "in deep water" (in trouble, or in a difficult situation) and "treading water" (literally: swimming on the spot, or figuratively: doing things in a routine and boring way, not making any improvements, putting in the minimum effort to just get by). If you wanted to combine the two idioms, there's a third that contains aspects of both: "keeping your head above water", which implies both the risk of drowning and the lack of progress.
keeping your head above water = garder la tête hors de l'eau
nager en eau trouble = in trouble, definitely (always figurative)
nager en eau profonde = in deep water (rarely figurative)
nager sur place = treating water (figurative)
nager entre deux eaux = between two worlds (figurative)
This has sort of been answered, but not quite fully in my mind, so I'm going to ask the question.
I understand that if we were to use dans, it would need to be followed by the definite article, at least in this particular case (or some other article in other cases), but I feel a chicken and egg problem coming along.
Do we use en because we use eau OR do we use eau because we use en? Also, why doesn't en need the article afterwards? Is there a historical linguistic reason for it? I'm very curious about this.
Usually "en" is a substitute for "dans le/la/les", which explains why it goes without an article. The preposition "en" is often used in fixed phrases which behave with their own grammar, and most often with immaterial things, like time (en novembre, en hiver, en 2017) and places (en France, en Europe).
"En eau profonde" is fixed and has figurative meaning, whereas "dans de l'eau profonde" has a concrete meaning.
Please take a look at other fixed expressions with "en": "en effet" (in effect), "en outre" (furthermore), "en revanche (however), "en cours" (in progress), "en aucun cas" (in no way), "en avance" (ahead of time), "en retard" (late), "en bonne santé" (healthy)... there are hundreds!
To clarify, when you say 'fixed' you mean that these are established phrases, not just things someone can just make up? And most (if not all) of these phrases that have nothing to do with time often are idiomatic in nature, or convey more than just the literal meaning?
I'm starting to like French. Ç'est trés bon!
Both words can be used to mean in a location, but "dans" is used before nouns that require an article:
- Je suis en eau profonde. = I am in deep water.
- Je suis dans l'eau profonde. = I am in the deep water.
- Elle est en classe. = She is in class.
- Elle est dans la maison. = She is in the house.
The two words can also be used to talk about things happening in time, and there are rules that determine which one to use. Here is a link: dans vs. en
Sitesurf explains a few comments above:
"In many cases, "en" can mean "in" in a figurative, non-concrete way, whereas "dans" is used with physical and material things." I think this is a solid way of knowing when to use it. I'm in deep water is not talking in this sense about literal water, but in the figurative sense. A bit like "I'm in deep shit".