I believe you may be narrowing a bit your question. Hydration is just one way in which we obtain the main solvent for our organic chemistry to work: water. We obtain lots of water from food as well. The key point I'm trying to make is to think of water as a solvent, not a source of hydration alone, because this will dictate the macro-molecular structure of your beings.
In Chapter 3 of Carl Sagan's "Cosmos" he hypothesizes what other organic chemistries that are not carbon based would be possible to sustain life (a very different type of life, of course). He basically boils life down to building blocks and solvents, using carbon and water as a start (i.e. our building blocks). The paragraph of interest is as follows:
I think the lifeforms on many worlds will consist, by and large, of the same atoms we have here, perhaps even many of the same basic molecules, such as proteins and nucleic acids - but put together in unfamiliar ways. Perhaps organisms that float in dense planetary atmospheres will be very much like us in their atomic composition, except they might not have bones and therefore not need much calcium. Perhaps elsewhere some solvent other than water is used. Hydrofluoric acid might serve rather well, although there is not a great deal of fluorine in the Cosmos; hydrofluoric acid would do a great deal of damage to the kind of molecules that make us up, but other organic molecules, paraffin waxes, for example, are perfectly stable in its presence. Liquid ammonia would make an even better solvent system, because ammonia is very abundant in the Cosmos. But it is liquid only on worlds much colder than the Earth or Mars. Ammonia is ordinarily a gas on Earth, as water is on Venus. Or perhaps there are living things that do not have a solvent system at all - solid-state life, where there are electrical signals propagating rather than molecules floating about.
It seems you are constrained to an acidic solvent, so your creatures would ideally have paraffin based structures (think "Alien"). I thought Sagan's ideas were quite applicable to your case!