Learn English – “I’m saturated” is correct and equivalent to “I’m overwhelmed”

The drink parallel of famished is parched.

parch
_{Dictionary.com main section}
5. verb (used without object) to suffer from heat, thirst, or need of water.
_{Dictionary.com "World English Dictionary" section}
2. (tr; usually passive) to make very thirsty: I was parched after the run

Dehydrated is a more clinical term, and would be parallel to malnourished, I think.

Both famished and parched can be used in both formal and informal contexts, although they're frequently used with a bit of hyperbole implied, which skews them toward the informal.

I'm so parched I think I could drink a river.

There are also a lot of idioms out there to signify extreme thirst, such as the "spitting cotton" one mentioned by CopperKettle, but if you're looking for the most straightforward parallel to famished, then you really can't do better than parched.

The chief pedagogical and administrative official in a U.S. K-12 school is indeed known as the principal, and this is the default term as well as the federal classification of the job.

Indeed it is, in many American dictionaries, the principal noun definition of principal. For example, AHD:

1a. One who holds a position of presiding rank, especially the head of an elementary school, middle school, or high school.

MW uses the broader sense in its full definition, but opens the summary definition with

the person in charge of a public school

Principal as both a title and occupation is almost universal in traditional K-12 state schools (i.e. public school), and no matter the official title of the official, this is the term by which the position will commonly be known. The title is not at all common in American postsecondary education.

There is considerable variation under other public and private educational models (e.g. charter schools, Catholic and other parochial schools, independent schools), and the principal may be known by a variety of other titles.

More than a few such schools adopted British terminology, regardless of whether the school itself follows any part of the British educational model; titles like headmaster / headmistress and head of school are uncommon but not unusual. But these are not interchangeable with principal, due to their connotations; an American is likely to assume a school with a headmaster is an expensive private school, possibly in New England and probably a boarding school.

In contrast, head teacher, which has become conventional in Britain, is relatively rare. A simple COCA search, excluding fiction, turns up the following counts:

• school principal 659
• headmaster 241
• head teacher 51

(It is difficult to search simply on head and on principal, due to their multiple common meanings. But this makes the prevalence of school principal all the more striking, as the other terms are far less ambiguous).