Bis

Bis
 

I know that bis is the word for encore.
I would like to know if it is used in situations outside of theater--such as
asking someone to repeat what they have said or asking a waiter for more water (bis de agua--for example). I know that in English encore is generally reserved for theater, but it French it is sometimes used elsewhere.

I don't know if the word bis is a lot used for the people, but I know that Bis and encore mean the same both word has the same mean in the dictionary, I found them in the dictionary of Tomisimo and the internet too, well if you know of some other kind of mean please let me know.

Encore is the French word for again. The Spanish equivalent is otra vez or de nuevo.
English borrowed the word for the theater and is used when we want to see something again or, more generally, when we want more of what we've seen/heard.

The Spanish equivalent for the English loanword is bis, as you stated.

Bis can also be used in Spanish as an adverb, where it means twice.
It also functions as a prefix, where it means two, or in words like bisabuelo.
I've seen it used to mean second, as in bis en clase.

Bis can be used in music, where it means repeat, as in:
bis dos últimos versos tres veces, luego bis último verso dos veces

In law, it means second. For instance, if an additional law were included BETWEEN existing laws 282 and 283, the new law would be called 282 bis.
Likewise, it can follow the house number in a street address, where it usually means that a second residence has been created where only one used to exist.

The borrowed phrase vis-à-vis (face-to-face) is rendered bis a bis in Spanish.

It was very interesting, that words are not very used right, because I never have heard in my life.

bisbisear is to whisper

bis would be the onomatopoeia for a whisper

Not very used nowadays